Report of the Chief,
Topographical Engineers, 1848
BUREAU OF TOPOGRAPHICAL ENGINEERS.
Washington, November 17, 1848.
SIR: In conformity with established usage, I have the honor to submit the following annual report of the operations of the corps since the last report, and an estimate for the duties for the ensuing year.
The peace with Mexico returned to the United States the large proportion of the officers of the corps which had been employed with the army in that country. The greater part of these were maimed with wounds, or sick from the fatigues and exposures which their duties required. Of their services in Mexico it is not necessary that I should speak. The reports of commanding officers pay frequent and brilliant compliments to their services, and the brevets which have been bestowed attest an accordance of the judgment of the Executive with these compliments. But, in addition to their regular corps duties, several of the corps occupied and exercised important military commands. Captain J. E. Johnston, of the corps, now brevet colonel in the army, in the exercise of his corps duties, until after the battle of Cerro Gordo, where he was severely wounded while reconnoitering the enemy's position, was afterwards made lieutenant colonel of the regiment of voltigeurs, and in that capacity acquired great reputation for the skill he displayed in the drill and discipline of the regiment, and for his gallantry in command on several important occasions. On the peace, he returned to his corps as a captain under a law of the last session and with the brevet of a colonel.
Captain G. W. Hughes, after important services in the duties of his corps with the army in North Mexico, and afterwards at Vera Cruz and Cerro Gordo, returned to the States emaciated and broken down by the climate, his fatigues and exposures. But rapidly recovering his health, he was placed at the head of a regiment of volunteers, and immediately went
back with his command to Mexico. His march from Vera Cruz to Jalapa is spoken of as one of great merit and severe trial, in which he on several occasions encountered and beat the enemy. He was then made military and civil governor of the department of Jalapa and Perote, and by his highly judicious, energetic, prompt, and well judged measures, was mainly instrumental in keeping that extensive district quiet as well as the whole road from thence to Vera Cruz. He continued in this command until termination of the war, when he returned to the United States, and has since resumed his duties in his corps, with the brevet of major.
First Lieutenant W. H. Emory. This officer accompanied General Kearny throughout his important and perilous march from the Missouri to the Pacific, as the chief of his engineer staff, executing also, towards the close of those operations, the duty of adjutant general to General Kearny's command. After the fighting in California had ceased, he was ordered back to the United States with despatches for the War Department. He was soon afterwards appointed the lieutenant colonel of Colonel Hughes's regiment of volunteers, (the Maryland and District of Columbia volunteers) and immediately joined him at Jalapa, with a part of that regiment which had not previously marched. He continued with Colonel Hughes until the end of the war, rendering important military services, after which he returned to the United States, and resumed duties in his corps, with brevets which gave him the rank of major. First Lieutenant Win. H. Warner. This officer was placed in charge of the ordnance train of General Kearny's command. He has also executed similar duties under Colonel Mason, in California, where he is at present, exercising the proper duties of his corps with the brevet rank of captain. He was severely wounded in the conflicts under General Kearny.
I have named these four officers because they were so fortunate as to obtain positions and exercise commands independent of and separate from their proper corps' functions, exhibiting the versatility of talent in the corps, and its ability to fulfil any military duties which it may be found necessary or proper to assign to it.
But there are other duties of the corps of less eclat, but not of less usefulness and importance, which shall now be reported.
All the interesting observations and reconnoitring made by the corps while operating with the armies in Mexico, are now being compiled in a map, under resolutions of the Senate, and will soon be completed, and be submitted to Congress. Of these examinations there has been already laid before Congress, Major Emory's report and map of General Kearny's march from the Missouri to the Pacific, and plans of the several engagements in which that command was involved; also Lieutenant Abert's map of New Mexico, and the report of his examinations of that country. These two reports add much to our geographical knowledge of that region of
the world, and furnish great facilities to any future operations in that quarter, whether civil, military, or commercial.
Accurate geographical and topographical knowledge of a country are particularly essential to military operations. They are the eyes of the commanding general. With these he can see the country, and can know how to direct and combine all his movements or marches, whether offensive or defensive, and without them he is literally groping in the dark, incapable of devising plans for his own operations, or of anticipating those of an enemy. With this knowledge, war becomes a science, in which intellect will ever predomidate over numbers; without it, war becomes the mere exhibition of physical force: slow, expensive, and often disastrous, as numbers and courage can alone be relied upon. Unless a knowledge of the country through which an army has to move is possessed, the army can act only on the defensive, and if this knowledge has to be obtained in the presence of an enemy, it is always at great loss of time, necessarily imperfect, and at great hazard of the services and lives of invaluable officers. Some of the most important movements and operations of the late war were governed by previous reconnoissances, made generally in advance of the army, and in the presence of the enemy, who might by his vigilance have interrupted or defeated them. We see, therefore, in these, as well as in hundreds of other instances which could be cited, the importance of geographical and topographical knowledge in army operations. Now this knowledge, a duty of the corps of tographical engineers to collect, can be well obtained only in time of peace. Peace is, therefore, the period which best enables a people to acquire the information necessary for the defence of their own soil, or to attack that of an enemy. From these general and important considerations it is no doubt owing, that in General Order 49, of the 31st of last August, by "the President of the United States," that this bureau is required to furnish officers of the corps of the commands of Oregon, California, New Mexico, and Texas. These are frontier commands, but lately the seat of war, exposed and even now threatened with hostile depredations from numerous bands of warlike and discontented Indians, long accustomed to domineer over those parts of Mexico and Oregon, now the possession of the United States, and whose tastes for plunder have been lately so often gratified without adequate chastisement, even nearer to us than the limits lately acquired.
These commands will probably require about twenty-five officers of the corps, and these officers can be of but little use, or can render comparatively but unimportant and unsatisfactory services unless means of making the surveys which may be considered necessary are allowed. The army can furnish escorts and safeguards, but it cannot furnish the means necessary for making surveys. Even in addition to its escorts, if it were able, which it is not, also to detach the numbers required for surveys, in
the various capacities of mechanics, chain-men, axe-men, boatmen, guides, and laborers, which these duties require, it could not furnish the requisite instruments, boats, tools, pack-horses, wagons, & c., &c.; and the men which might be detached are rarely of the kind qualified for such duties, while such detachments are destructive of discipline and of usefulness in their proper corps. Economy of cost, and the well-being of these duties, do therefore most eminently call for some arrangement by which such duties can be performed, independent of calls upon the army, except for escorts and safeguards. In my long experience as an officer in the field, as well as at the head of this bureau, in which first capacity I have operated with men detached from the army, but two modes have suggested themselves as adequate to meet the difficulty.
One is that which the government has now for so many years adopted, namely, the making of small annual appropriations to meet the contingencies of a survey. The second is that of enlisting men specially adapted to these duties. Although this last is the practice of other countries, it has never been adopted by us. It is without doubt the better course, admitting, as it does, of the most economical, the most prompt, and the most intelligent execution of the duty, reducing the contingencies of a survey to those smaller items, independent of the pay and support of the class of mechanics and others as before enumerated, which have now to be employed temporarily, and at far greater cost, and whose experience and the facility and knowledge acquired in the duties are continually lost by frequent changes, which the temporary nature of their present employment involves.
But inasmuch as this latter course has not been adopted by the government, I can submit no estimate in reference to it, and shall on that account submit estimates in conformity with established usage.
As before remarked, the commands of Oregon, California, New Mexico, and Texas,
have to be supplied with officers of the corps, and surveys have to be made
in those commands.
I therefore respectfully submit for considerations-
|For military surveys in Oregon||$10,000|
|For military surveys in California||$10,000|
|For military surveys in New Mexico||$10,000|
|For military surveys in Texas, and from the navigable waters of the Red River to the Rio Grande||$15,000|
Our knowledge of the Red River above Nachitochez is more general than precise, but there is every reason to believe that its capacity for boat navigation extends far into the interior of Texas, even as high as old Fort Washita, to which point, and above it, it is represented that two feet of water can be carried throughout much of the year. These facts make that river a line of great military importance in reference to the defence of
that frontier, and if correct, will enable the government to establish a series of military posts upon that river, and to be supplied from it in the very heart of the Camanche country. And if from the head navigable waters of this river a good military road can be traced to the Rio Grande, its facilities in the defence of that frontier will be invaluable, as well as in whatever relates to the defence of New Mexico by ready and easy access to that quarter, and by such means of more fully developing its agricultural and mineral resources.
These distant military posts and military roads are the pioneers of civilization and of wealth, by the protection they afford to remote settlements, the value they give to public lands, the encouragement to cultivation by the consumption of produce, and by the intelligence and good habits diffused by such a nucleus of well-informed and orderly persons of both sexes as generally constitute the population of our garrisions.
The usual surveys in reference to the military defences of the frontier, inland and Atlantic, have to be attended to. These are generally of positions to be fortified and of their approaches, upon a scale sufficiently large to plan the works required, and embracing all those details collected by no other surveys, necessary to determine upon the true position and probable cost of the contemplated work. For these objects a small amount of ten thousand dollars is only required, as there is an unexpended balance of a former appropriation.
The survey of the lakes has been pushed forward as rapidly as circumstances would admit. The large proportion of the corps required for the armies in Mexico, obliged a rather restricted employment upon this survey during the last season, but the whole of that intricate navigation at the western end of Lake Erie, between a line from Sandusky to Point Pelee, and thence west to the mouth of Detroit river, with its several islands and shoals, has been thoroughly surveyed, and the maps and charts are now being made.
The collection of lake surveys has become so numerous, under the various appropriations which have been made, that the office is now ready to issue an atlas of charts which would be of great aid to the commerce of the lakes. The cost of engraving a suitable edition would not exceed five thousand dollars, for which an estimate is respectfully submitted. The advantage of such a publication would be invaluable, and would give to the great and increasing commerce of the lakes those guides of which it now stands so much in need. No additional estimate for the survey of the lakes is submitted. The late period of the last session of Congress at which the existing appropriation was made and the restricted operations as before described, have left a sufficient balance for the operations of the next season, which, together with the desire of avoiding all demands which the well being of public service shall not make extremely necessary, have induced me to omit any additional estimate on this account for the ensuing season. It is contem-
plated, in the course of the ensuing season, to make a geographical connexion between the survey of the lakes and the Atlantic coast, by means of the magnetic telegraph, which now extends to Buffalo, Detroit and Chicago.
A law of the 3d March, 1847, assigned to this office the construction of several light-houses.
In the annual report of November 22, 1847, these are all referred to in so much detail, that it leaves but little now to be said in this report.
Light-house on the Whale's Back rock, Portsmouth, New Hampshire.
In the report of last year, the light house on this position is minutely described, the plan of construction, and the defects in the plan. It is there stated that the repairs of this work would involve a cost about equal to that of a new iron pile structure, and would in the end be a patched structure, and would probably fail in meeting just expectations. It is also stated in the same report that as fears of "immediate danger to the present structure are not entertained, no work has been commenced." Other reasons induced a delay in the work at this place; these were to await the experience of erecting an iron pile light upon a much more exposed position, Minot's Rock, Boston harbor. Having now overcome the chief difficulties in the work on Minot's Rock, another careful examination of the Whale's Back Rock light will be made in the ensuing spring, when it will be decided whether the "rebuilding" directed should be farther postponed or be immediately commenced.
Lighthouse on Minot's Rock, Boston harbor.
This has been a work of extreme difficulty, and of no little danger, and the results are a singular exhibition of the triumphs of perseverance and mechanical ingenuity. The rock is exposed to the whole burst of the Atlantic wave. A small portion of it, involving a circular area, rarely exceeding 25 feet in diameter, is bare at low water and during very calm weather. But no part of this area is more than three feet above extreme low water, and during slight winds the sea breaks over the whole with great violence. Upon this small and extremely exposed position, a footing had to be obtained, and holes had to be drilled in the rock, in which were to be insetted the iron piles to sustain the structure. This short description will sufficiently apprise all those who have any knowledge of a sea shore of the serious and continued difficulties of working on such a place. It gives me great pleasure to add that no lives have yet been lost in the work, although there have been several accidents, and additional pleasure to say that all the piles to sustain the work have been established, as well as the skeleton iron frame of the top, intended to connect the piles and to sustain the keeper's house and lantern. All serious difficulties are therefore overcome.
The work has been under the superintendence of Captain Swift of the corps, and the resident agent and contractor was Mr. Benjamin Pomeroy, a person of the most extraordinary perseverance and inexhaustible ingenuity, and well acquainted with working in such positions. The report of Captain Swift is hereto added as an appendix. A small appropriation of 4,500 dollars is now required to procure and complete the illuminating apparatus for this lighthouse, which I believe will be found to be one of the most useful on that coast.
Brandywine Shoal light.
This structure is on a sand bar in the mouth of Delaware Bay. The lower tier of piles are all in place braced and connected, so that in reference to this work, it may also be said that its chief difficulties are overcome. The work will be left in this condition before the superstructure is put up, in order to see the effect of winter storms and of floating ice upon it. As the report and estimate of the superintending engineer, Major H. Bache, has not yet been received, I am necessarily obliged to delay any further notice of the work, or additional estimate to a future time.
Carys fort reef light-house.
This is also an extremely difficult position upon the Florida keys, and is to be made upon iron piles sunk into the rocky soil of the reef. The reef has been carefully examined, the structure is being prepared, and it is contemplated that during the month of December the materials and frame will be transported to the reef, and the erection of the building be commenced.
Sand Key light-house
It was so late a period during the last session that the difficulty in the law in reference to this work was removed, but little more has been done than to survey the position. Moreover, it is extremely desirable to profit in the erection of this light house by the experience which will be acquired in the erection of the one on Carys Fort reef.
Wangoshance Shoal light-house, straits of Michigan.
We have succeeded in establishing the pier work, essential to the protection and construction of this work, and also the concrete foundation within the piers, upon which the keeper's dwelling and lighthouse are to be erected.
All these structures are works of extreme difficulty, in much exposed positions, requiring great care, great energy, untiring perseverance, and more than common mechanical resources in the superintending engineer. The success which has attended our efforts, as already described, is proof that these qualifications have not been wanting, is the best compliment upon the plans which have been pursued, and justifies the anticipation that the whole of these works will in good time be completed, and will be permanently established.
The construction of the lighthouse at Monroe, Michigan, an assignment to this bureau, at the request of the Treasury Department, is nearly completed. The superintending engineer reports that it will be finished during the ensuing month of December.
Sea wall for the protection of Fairweather island,
near Black Rock, Connecticut.
A part of the small balance of the appropriation of 1847 was expended in the construction of this wall early in last December, when it was inspected and received, and the rest of this small balance was expended in May, 1848, in repairing an old wall formerly put up at this place by the Treasury Department, for the protection of the light keeper's house.
The late period at which the appropriation of 1848 was made, necessarily run the work late in the season. 700 perches of the wall had been laid by the 1st of November, leaving about 1,200 more perches yet to be put down. Of these about 600 perches will probably be finished during the present month; the balance of the work will have to be suspended until after the ensuing spring.
In addition to these duties, an officer of the corps, Lieutenant Colonel Turnbull, on application from the Treasury Department, has been assigned to superintend the building of the custom-house at New Orleans. And, on application from the same department, this bureau has been authorized to superintend the construction of a marine hospital at Chicago, one at Paducah, and one at Natchez. The additional estimates which these works require will be submitted to the consideration of the Treasury Department, as the work, although now a duty of this bureau, is, from the wording of the law, under the superintendence of that department.
An officer of the corps, Major J. D. Graham, is occupied, under the State Department, in efforts to restore the maps of the northeastern boundary, which were destroyed by fire. He has three assistants from the corps temporarily assigned to him.
On an application from General Brooke, two officers of the corps were assigned to him for the purposes of making a military reconnois-
sance of the upper Mississippi, with a view of establishing certain frontier posts, and to make the surveys of the localities which should be selected. The duty will be completed during the present month.
There was a resolution of the House of Representatives, dated August 8, 1848, directing the Secretary of War to have a "survey and examination made of that part of the Potomac river between the Long bridge and Georgetown, with a view to ascertain the cause of the formation of land on the flats along the banks of the river, and that he cause also an estimate to be made of the cost of repairing the Long bridge; and also of constructing a bridge across the Potomac at the aqueduct of the canal at Georgetown, and also an estimate of the probable cost of keeping up a steamboat ferry in the place of the Potomac bridge, and that the report be made at as early a period in the next session as practicable."The execution of this resolution will of necessity be very imperfect without making the survey as directed, and this survey, in order properly to elucidate the questions involved in the resolution, should extend as far below the bridge as Alexandria. But there is no appropriation out of which the expenses of the survey, directed to be made, can be met; and it does not appear to have been covered by any appropriation during the session in which the resolution was passed. Under these circumstances, I am not aware of any other course to be pursued than to submit to the consideration of the department an estimate for the survey directed to be made. Since the Long bridge was erected, the river has experienced very serious modifications in its shoals and channels, immediately adjacent to the bridge and below it, as well as above the bridge. All these changes should be minutely ascertained, and carefully delineated, before an intelligent and reliable report, under the resolution, can be made. But, inasmuch as the expenses incident to the resolution cannot be met without an appropriation, an item for three thousand dollars on that account is submitted.
Appropriations for various streets and avenues of the city.
As it was only those streets, or parts of streets, directed to be paved, which were placed under the War Department, it will be only of these upon which any report will be made from this office. It was late in the season when these appropriations were passed, and, in addition, it was directed that the work should be done by contract, after thirty days' notice to bidders in the cities of Washington, Baltimore, Philadelphia, and New York. This change in the system involved many serious and injurious delays: in the time necessary to prepare the advertisements, in the notice of thirty days required to be given, in the examination of the bids and the making of the contracts, and in the preparations for work, as no bidder could make the requisite preparations until after he was assured
that he would obtain the contract. These causes of delay absorbed so much time as to render it comparatively impossible to complete the work this season, as, from these causes, it could not be commenced before the 9th day of October. Without these delays, more than half of the work would have been completed by the day, when, owing to these delays, the work had to be commenced.
The system heretofore has not been to do such work by contract, except for materials and particular parts in which the contract system could be adopted to advantage, and I venture, without fear of error, to say that, in reference to economy of cost, energy of execution, and quality of both work and materials, that the paving heretofore done will compare advantageously with that of any part of the country.
The appropriation for completing the centre strip of the avenue is inadequate to the work, as it does not cover the low bid at which the contract is made. A small item, to meet this deficiency, and to cover charges for overseers and superintendents, is submitted, amounting to $1,200.
There is also additional work to that contemplated in the appropriation for fifteenth street, which will cost about $1,500, and also a sewer or drain under fifteenth street, which will cost about $2,160. This street is the drain of large bodies of water, requiring an underground sewer or drain sufficient capacity. To pave the street before constructing this drain would be an extravagant mode of proceeding, as much of the pavement will have to be taken up, and the ground re-excavated, in order to make the drain at any future period, at an increased expense, which will nearly double the cost at which the work can now be done; and, as I fear we will not be able to do the paving of fifteenth street this winter, an estimate for this drain, of $2,160, is respectfully submitted to your consideration.
In doing the pavement that has been ordered, the side walks are of necessity taken up to some extent, and seriously deranged in their slope. I allude now particularly to the side walks on the streets in front of the executive buildings. These side walks, badly bedded when first laid, are also much worn and broken. It is respectfully suggested that these should be relaid. The cost will be about $6,000.
Seventeenth street, the street west of the war office, is so intimately connected with the work now being done, under the laws of the last session, that the work will necessarily be imperfect and liable to serious changes hereafter, unless seventeenth street be included in the operation. This street, like fifteenth street, is the drain of vast bodies of water, and will require a large culvert, and the whole surface of the street to be modified to a different grade. The work should extend to the south of the present Navy Department lot, and will cost about $13,000.
An estimate, in accordance with the expositions of this report, will be submitted to your consideration.
Respectfully, sir, your obedient servant,
J. J. ABERT,
Colonel corps Topographical Engineers.
Hon. W. L. MARCY,
Secretary of War.
P.S. The estimate was made in conformity with this report, but was afterwards modified by direction of superior authority.
WASHINGTON, November 4, 1848.
SIR: I have the honor to make the following report upon the several works enumerated below, which, by the orders of the bureau, are entrusted to my superintendence:
1. Lighthouse on Whale's Back, harbor of Portsmouth, N. H.
The report which was made on the 2d April, 1847, contains the reasons which induced me to recommend that no steps might be taken towards the rebuilding of the light house at the Whale's Back until the light at Minot's rock, in Boston harbor, should be in a state of forwardness.I represented, in the report above referred to, that the old light was in no immediate danger; and I doubt not now that it may answer all the purposes of a new structure for some years to come; still, it would be proper to have another careful inspection of the building made in the ensuing spring, when it could be determined whether the rebuilding should be further postponed or not.
2. Minot's Rock lighthouse, Boston harbor, Mass.
At the date of the last annual report (October 15, 1847) the condition of the work at the Minots was stated, and some of the difficulties which attended the operations of that season were specified. As the frame or main structure may now be considered completed, a brief description of the work and some details connected with it during the progress of construction, may be regarded as not uninteresting.
Minot's Rocks, or, as they are generally designated, "the Minots," lie off the southeastern chop of Boston bay, about seventeen miles from the city, and something less than eight miles from the Boston light.These rocks or ledges, with others in their immediate vicinity, are known as the "Cohasset Rocks," and have been the terror of mariners for
a long period of years; they have been, probably, the cause of a greater number of wrecks than any other reefs or ledges upon the coast, lying, as they do, at the very entrance to the second city of the United States, in point of tonnage, and, consequently, where vessels are continually passing and repassing. The Minots are sunken, and bare only at one quarter flood, and the trend of the coast in that direction from Boston bar being southeasterly, vessels bound in, with wind heavy at northeast, are liable, if they fall to leeward of Boston light, to be driven upon these rocks.
As evidence of the great necessity of a light at these dangerous rocks, I have in my possession, from a reliable source, a statement of the number of vessels, with their names and tonnage, which have struck upon the Cohasset rocks within the last thirty years, but mostly, as my informant remarks, within the last fifteen years, to wit: ships, 10; brigs, 14; schooners, 16; sloops, 3; total 43. Of these, 27 were a total loss. From all this, it may be clearly inferred that it became necessary that these hidden dangers should be pointed out to the seamen, and, instead of the fatal breaker to give him the first warning of his approach to danger, that there should be a friendly beacon erected upon the rock, to guide him in the storm, and enable him to avoid the horrors of shipwreck; and these, doubtless, were the considerations which led to the enactment of the law for building the lighthouse in question.
The rock selected for the site of the lighthouse is called the "Outer Minot," and lies farther seaward than others in the group known as the Cohasset rocks. At extreme low water, an area of about thirty feet in diameter is exposed, and the highest point in the rock is about three and a half feet above the line of low water. It is very rare, however, that a surface greater than twenty-five feet in diameter is left bare by the sea. The rock is granite, with vertical seams of trap rising through it.
From observations upon the tides, made at Boston light house by the coast survey, from June 7th to October 27th, 1847, the following results were obtained; and, by the kind permission of the superintendent, communicated to me, together with a tracing of the coast from Boston light to Scituate light.
|Rise of highest tide||14 feet 7 inches|
|Mean rise and fall of tides||9 " 4 "|
|" " " spring tides||10 " 8 "|
|" " " neap||8 " 3 "|
The form of the lighthouse frame is an octagon, of 25 feet diameter at base. The structure is formed of eight heavy wrought iron piles, or shafts, placed at equal distances from each other, with one, also, at the centre. These piles were forged in two pieces each, and are connected together by very stout cast iron or gun metal sockets, the interior of which is bored, and the pile ends are turned and secured to the sockets by means
of large steel keys passing through the piles and the sockets. Above and below the joints, or sockets, and connecting the middle pile with each outer pile, there extends a series of wrought iron braces; and the outer shafts are connected together to similar, extending from one to the other, and thus the whole structure is tied together. At each of the angular points in the octagan and at the centre a hole of twelve inches in diameter and five feet in depth is drilled in the rock, the outer holes with the inclination or batter given to the outer piles and the middle holes vertical.
The surface of the rock being irregular in shape, and the holes in each case five feet deep, it is evident that the piles must be of unusual lengths, the least length in the lower series is thirty-five and a quarter feet; the greatest is thirty-eight and three-quarters feet, and the others are of various lengths between them. The piles in the upper series are of uniform length, viz: twentyfive feet each, the inclination or batter of the piles towards the centre is such as to bring the heads of the upper piles within the periphery of a circle of fourteen feet diameter, and there, at an elevation of sixty feet above the base of the middle pile, or fifty-five feet above the highest point of the rock, the pile heads are secured to a heavy casting or cap, to the arms of which they are securely keyed and bolted. The middle shaft is eight inches in diameter at foot and six inches at top, and the outer shafts are eight inches at foot and four and a half inches at top. All of these are forged ten inches in diameter, at the point where they leave the surface of the rock and taper uniformly down to eight inches diameter in both directions, within a distance of five feet. The lower braces, placed nineteen feet above the rock, are three and a half inches in diameter; the second series, nineteen and a half feet above the first or thirty-eight and a half feet above the rock, are three inches diameter, and a third series, introduced eight and a quarter feet below the cast iron cap, to form the support of the floor of the store room, is made of two and half inch square iron.
The outer piles being inclined towards the centre, and the piles and the braces being inflexible, it is clear that, so long as the braces remain in place, the pile cannot be withdrawn from the hole, for the whole structure acts as an immense "luvis;" either the braces must be ruptured, or the rock itself must yield, before a pile can be displaced.
Upon the pile-heads are cast-iron sockets, furnished with arms three feet in length, pointing outwards. These sockets are keyed to the head of the piles, and are bolted to the arms of the cap or spider, flush with its upper surface; thus giving a diameter at top of 20 feet from out to out. The object of the arms is to afford support for a footway or gallery outside of the keeper's house, which is placed immediately on the cap, and there secured by bolts and keys.
The keeper's house is octagonal in shape, and 14 feet in diameter; the uprights or stanchions are of cast-iron, and rest upon the cap immedi-
ately over the pile-heads, where they are secured with bolts and keys; these uprights are cast with double flanches, between which two-inch plank, tongued and grooved, are to be fitted horizontally, and at right angles to these another series of plank is to be set on end or vertically, and, together, these form the side or frame of the house; upon this frame the roof will be placed, and, finally, upon this the lantern will be set up.
The drilling of the holes in the rock for the lighthouse occupied the better part of two seasons. The erection of the iron structure in place, it may be conceived, was comparatively a work of much less difficulty, and, with favorable weather, an undertaking requiring not much time. That some of the difficulties may be known of working down 9 holes of 12 inches diameter and 5 feet in depth, in a rock of granite traversed by veins of the most obstinate trap, in a situation exposed to the delays produced by every breeze which had east in it, I will enumerate briefly, from the journal of operations kept at the rock, some of the details, for future reference.
Early in April, 1847, I invited Mr. Benjamin Pomeroy, the contractor who had in 1843 erected for me the Black Rock beacon, in Long Island sound, (a structure built upon the same principle that the Minot Rock light is built upon,) to accompany me to Cohasset, with the view of inducing him to undertake the drilling of the holes by contract, and also to take the piles, braces, and cap at Messrs. Alger & Co., South Boston, where the work was to be executed, and to erect them in place at the Minot. After waiting eight days at Cohasset for a favorable opportunity to examine the rock, we effected a landing, and, with the advantages of a smooth sea and a very low tide, made sufficient measurements to determine the probable area of sound rock which might be relied upon for the base of the proposed lighthouse
The proposition made by Mr. Pomeroy, to drill the holes in the rock for the reception of the piles for the lighthouse, I considered too high, and consequently I declined it and sought elsewhere for a competent individual to undertake the work; after advertising in the newspapers, I received proposals from Mr. James Savage, and entered into an agreement with him to drill the holes, but after some weeks' delay Mr. Savage abandoned the contract; I then recommended and was authorized to accept the proposals of Mr. Pomeroy, and he undertook the work at once, but by the failure of the first contractor the greater part of the best portion of the season, 1847, was lost, and it was not until July 22, that the new contractor, Mr. Pomeroy, actually commenced work upon the rock.
The mode of working the holes down had for sometime occupied the thoughts of the contractor, and he became satisfied that holes of the magnitude required in that exposed situation, where the sea was so continually breaking over the rock, could be drilled by machinery only, and that
it would be necessary to have that machinery elevated beyond the ordinary reach of the sea.
The drill used was of a peculiar form, with an edge in shape somewhat similar to the letter z, made of the best cast steel, and fitted to an iron shaft some 30 feet in length, and weighing, with the drill attached, about 600 pounds.
The machine for working the drill was a wheel and axle furnished with tooth and pinion, and a crank or windlass at each end; this was placed on a frame of stout oak, and it required the power of four men to work it effectively. A cam and a fly wheel were attached to the axle, and at every revolution the drill was raised about eight inches, and driven ordinarily at the rate of about fifty strokes per minute, the men being relieved every twenty minutes.
To support this machine, it was necessary to erect upon the rock a triangle or shears of very heavy spars, secured at their feet by means of pintles, and chained down to Lewis bolts inserted in the rock; upon the triangle was placed a platform, and upon this the machine was worked, the drill being kept at the proper degree of inclination for the hole by means of guides, through which the shaft moved up and down; the whole arrangement answered the purpose admirably well, and the holes were cut as truly and as perfectly as an auger hole could be cut in a piece of wood.
The triangle and drilling machine were swept from the rock twice by the sea during the first season's operations, and the men were frequently washed from the rock, but happily no lives have been lost. The work was suspended at the rock on the 25th October, 1847, and by reference to the journal of operations, noted carefully day by day, it will be seen how short a space of time can be reckoned upon for work in a situation so exposed.
In the report of the contractor of the 8th November, 1847, accompanying the journal of operations for that season, is the following remark:
"It will be seen by my journal, that from the 22d July to the 25th October, I was able to land on the rock, to do work, only 25 days, viz: 5 days in July, 13 in August, 7 in September and none in October. The whole number of hours we did actually work on the rock was only 120 hours, of which 53 were from the triangle when we could not stand on the rock to work."
The total number of men employed in 1847 by the contractor was 34, the average number about 21; in addition, a schooner of about 80 tons burthen was chartered by the contractor for himself and his hands to live on board of, and the vessel was kept moored near the rock at all times when she could lie there in safety, or when the weather would admit of it; by this arrangement every hour of time, in which work could be done at the rock, was rendered available.
All the necessary preparations for the work of the present season were made early in the spring; a new triangle was provided of heavy spars,
some forty-five feet in length, and strengthened by a number of very stout iron braces, and with bars of iron on each spar, extending over all that part of the triangle which was exposed to the shock of the sea; a vessel and hands were employed by the contractor, but no work upon the rock was effected until the 18th, 19th, and 20th May, and from that period until the 3d and 5th of June nothing was done, the weather and sea preventing even a landing. Between the 14th and 29th of June the sea generally was smoother, still there were several of the intervening days on which little or nothing could be done; from 29th June to 19th July, but three landings were made, and at these times the sea ran so high there was but little work accomplished.
On the 21st July, this remark is found in the journal: "To day and yesterday worth more for work on rock than last four weeks."
The holes were all finished on the 16th August; that is to say, 9 holes of 12 inches diameter, 5 feet deep each.
Some delay was produced in this stage of the work, by an alteration which I had decided some time earlier in the season to make, to wit: to increase both the size and the length of the lower series of piles, and this increase in dimensions produced some delay in the forging at the machine shop. The difference in size between piles of hammered iron 25 feet long and 8 inches diameter, as originally designed, and piles 35 feet long and increased to 10 inches diameter, the size ultimately adopted, involved some difficulties, and required a little more time in the fabrication than I had reckoned upon, so that it was not until the 2d September that 6 piles of the lower series were forged.
On the 4th and 5th September, these 6 piles were erected in place, and, by the 21st, the three remaining lower piles had been placed, and three of the braces belonging to that series placed also.
From the 21st September until the 7th October, no landing could be effected upon the rock. On that day the middle pile of the upper series was placed in its position; on the 10th October two more were put up; on the 12th five more, and on the 16th the last pile of the upper series was set in its place. On the 26th October, the cap, or spider, a casting to rest upon the heads of the piles to receive the dwelling house of the keeper and the lantern, consisting of eight arms and weighing some five tons, was hoisted partially towards its place, and on the 30th October this difficult undertaking was successfully completed, and the spider fixed in its proper position and secured there, at an elevation of fifty-five feet above the top of the rock.
The Boston light being a revolving light, and the Minot being the next in order upon the coast, should be a fixed light; accordingly the apparatus ordered is of that character, and is composed of fifteen brass lamps, with reflectors of 21 inches diameter in the clear, With very heavy plating of silver, and the best description of work.
The framing of the lantern is of wrought iron; and is a polygon of sixteen faces, diameter at the angles eleven feet six inches, height six feet six inches, furnished with cast-iron ventilator, the glass, French plate, forty-four inches by twenty-four inches, and three-eighths of an inch thick; the extent of the illumination will be two hundred and ten degees.
Thus it will be seen that the entire height of the structure from the surface of the rock to the top of the lantern will be about seventy feet, and upwards of fifty feet above the line of highest water.
The weight of iron work in the shafts, braces, couplings, collars, spider, or cap, and columns for keeper's house is nearly seventy tons; of this upwards of forty tons is wrought iron, and the residue of cast iron; the average weight of each complete shaft is about 8,200 pounds; that cast iron couplings for connecting the upper shafts with the lower are three feet long, and weigh nearly 800 pounds each; they are made of the best gun metal. The weight of the lantern and illuminating apparatus will be about four and a half tons. The lantern, lamps, reflectors, and other fixtures for the lighthouse will cost four thousand five hundred dollars, as will appear by the detailed estimates of same, rendered on the 24th ultimo.
Below the keeper's house, and enclosed within the pile heads, a species of cellar, or store room, of the size of the house, is to be built, to contain oil, fuel, provisions, &c. I had hoped last season that all this might have been accomplished before the boisterous weather of the present year came on, and the light brought into use this winter; but this has not been practicable, as the journals of operations will clearly prove.On the other hand, it may be considered not unwise to allow the skeleton structure to stand through one winter exposed to the fury of the sea, before the light house is fitted up with its illuminating apparatus, and before it is occupied by a keeper.
3. Sea-wall for the protection of Fair Weather island, near Black Rock, Connecticut.
The balance of the appropriation of 1847, except $108, was expended in the construction of the seawall before the 1st December last, and it was inspected and accepted by me on the 7th of that month, the work having been faithfully executed, according to contract, under the superintendence of Seth Perry, esq., the agent. In May, 1848, $105, remaining of the appropriation of 1847, was expended in repairing the wall heretofore built, under the direction of the Treasury Department, for the protection of the light keeper's house.
The late period at which the appropriation was made for the completion of this work, (12th August, 1848,) will prevent all the stone work, for the protection of the island, from being laid before the close of season.
On the 1st November instant, seven hundred perches had been laid, and there remains to be laid about 1,200 more; of this, perhaps one-half, or six hundred perches, will be finished during the month of November, and the residue must be suspended until the ensuing spring.
Very respectfully, sir, your obedient servant,
M. H. SWIFT,
Captain, Topographical Engineers.
Colonel J. J. ABERT,
Chief, Topographical Engineers.
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