intensity of action of several of the modern explosives, when exploded under water in torpedo cases, is given as a sample of the work:

It should be added that, for various reasons not necessary to discuss, the board is agreed that dynamite No. 1 should be adopted for our serv ice.

To illustrate the precision of analysis rendered possible by the formulæ deduced from the data collected, the following example is given; The problem is to determine the crater radius (r) which will be produced in ice from 8 to 10 inches thick, by the explosion of (c) pounds of a modern explosive, of which the constant is (E) submerged (S) feet below the surface, the angle from the nadir to the line of fracture being (6). For dynamite No. 1 the numerical value of E is 186. The formula

are:

S

r= cos (180-6)

10.49S2.1

(6+E) cos2 (180-6)= с

Twenty-one trials were made with dynamite No. 1, dualin, and guncotton, with charges varying from 1 to 10 pounds, and submergences varying from 2 to 13.5 feet, and crater radii varying from 0 to 14.1 feet. The maximum discrepancy between observation and the indication of the formula was 1.2 feet in the crater radius, the mean discrepancy being 4.5 inches.

Thirty-five shots have been fired in the submerged ring, chiefly to test new explosives; and this work will be continued during the coming sea

son.

Many experiments have been made with electrical fuzes, employing original methods and apparatus. The object has chiefly been to detect any deterioration due to long storage. The result has shown that our adopted patterns exhibit none, and some of the samples have been on hand eight years.

One of our buoyant mines, after being submerged in the channel off Willets Point for four years and five months, has been found to be in a perfectly serviceable condition, thus sufficiently proving its trustworthy character.

Attention should be invited to a very compact and simple dynamoelectric machine made by the Laflin and Rand Powder Company. The cost is only twenty-five dollars, and the instrument is admirably adapted for use as a portable igniting apparatus for torpedoes and heavy ordnance. It has been carefully tested by practical use at Willets Point during the past two years.

A supply of torpedo cable insulated with kerite and made in this country has been purchased for trial during the past year. The insu lation is low, varying from fifty to one hundred megohms per mile, but the material promises well in respect to permanence. Time alone can

properly test its value, and measures have been taken to determine this important point.

Experiments have been continued with the electric light to test its value as a means of protecting our mines against operations of the enemy. The results upon the whole are satisfactory.

To determine the destructive range of countermines which may be employed by an enemy against our mines, a charge of 500 pounds of dynamite No. 1 was exploded last autumn. This charge was contained in an iron torpedo resting just above the bottom in water 20 feet deep. It was surrounded by our service mines at various distances, and the result proved that its power of injuring them was far less than the esti mates given in foreign journals. A charge of eight pounds of dynamite No. 1, contained in a cast-iron shell, was placed at a horizontal distance of 40 feet from the exploded charge, and was not detonated by sympathy. It was subsequently cracked open by a charge of half a pound of dynamite laid upon it when supported upon a rock in the air, and the charge (8 lbs.) was thus recovered quite uninjured. This experiment has been repeated several times, and in no case has the charge been fired. Charges of one pound of dynamite contained in tin cases were suspended at various distances from the great mine, and even when crushed at 80 feet, were not fired by sympathy. These experiments seem to prove that the danger of sympathetic explosion of mines charged with dynamite has been greatly exaggerated in Europe.

To obtain some precise data upon the manner in which the forces developed by a subaqueous explosion act upon a vessel, an old schooner was blown up last autumn at Willets Point. Her name was "Olive Branch"; length, 71 feet; tonnage, 60 tons. She was anchored in water 15 feet deep. Two torpedoes, each a beer-keg containing 50 pounds of mortar powder, were suspended 10 feet apart and 3 feet below her bottom amidships. They were submerged 7 feet. Six cameras were placed at a distance of about 500 feet, so arranged that by the aid of electricity instantaneous views could be taken at the pleasure of the operator. The time of explosion and of dropping each camera slide was electrically recorded on a field chronograph. The torpedoes were exploded simultaneously. A picture taken one-tenth of a second thereafter showed the bow and stern plunged in the water, and the middle of the vessel raised about 16 feet in the air. The masts were still vertical, and the jet of water had reached a height of about 70 feet. The second picture, taken 1.5 seconds after the explosion, showed a column of water 160 feet high, containing many fragments of the wreck. The third picture, taken 2.3 seconds after the explosion, showed the jet at its maximum, 180 feet high. The air was full of fragments, but apparently none had yet begun to fall back to the water. The fourth picture, about 3.3 seconds after the explosion, exhibited a descending mist; the water agitated by heavy splashes of fragments, and the site of the wreck shrouded by a cloud of smoke. The fifth picture, taken a second later, showed only a thin cloud of mist and smoke, with no evidences of violent action remaining.

Thus the total destruction of the schooner had only consumed about 0.1 of a second, and the whole exhibition of power only about 4.5 seeonds. The exceedingly short duration of the destructive action leaves no doubt that upon the mean and not upon the maximum intensity of action (pressure), will the useful effect probably depend.

The purchase and storage at our forts of the material approved for the torpedo defense of our harbors has continued during the past year so far as permitted by the limited appropriations granted by Congress.

It should be understood that large sums can now be judiciously expended, and that, in the present unsatisfactory condition of our heavy ordnance, as presented in the reports of that department, the safety of our coast may depend largely upon having a suitable supply available for immediate use.

RECOMMENDATIONS BY THE BOARD.

It is the duty of the board to again invite attention to the urgent necessity of increasing the number of enlisted men of the Battalion of Engineers sufficiently to enable them to properly perform the new duty assigned them by Congress of acting as a Torpedo Corps for the defense of our extended coast. The minimum force consistent with reasonable efficiency has been carefully estimated at 520 men, and the number now available is only about one-fourth of that figure. No increase in the legal organization nor in the number of officers is required. A provision, authorizing the President to recruit the companies to the standard now authorized by law, will supply the needful number. The duty is perhaps more technical than any other in the Army, and requires special qualifications and special training; and the men are equally as available for other duties in an emergency as those enlisted in the other three combatant arms of the service.

The board would renew its recommendation that a special appropriation be requested for preparing our forts for operating torpedoes. At the outbreak of hostilities it will be too late for this work to be properly done; the cost is small; the necessity is evident. An appropriation of $100,000 would suffice to place many of the more important works in an efficient condition for this service.

For the purchase of torpedo materials, and for instructing the engineer troops in the use of the same, and for continuing the trials designed to perfect the system, an appropriation of $100,000 is recommended.

SPECIAL DUTIES OF INDIVIDUAL MEMBERS.

In addition to their duties in connection with the Board of Engineers for Fortifications, the individual members composing the board have, as usual, been much engaged as members of other permanent and special boards.

As in previous years, Colonel Barnard has continued to serve as a member of the Light-House Board, and throughout the past year has presided over the Board of Engineers constituted by S. O. 71, H. Q. C. E., July 8, 1878, to take into consideration the improvement of the low-water navigation of the Mississippi and Missouri Rivers, and to submit a plan therefor. By direction of the President of the United States. and in accordance with section 4 of the act of Congress approved June 19, 1878, he served as senior member of a board of engineers required to examine the works in process of construction at the South Pass of the Mississippi River, and report upon progress made, probable cost of completion, results produced, and that may probably be produced, probable permanency of the works, and advisability of any modification of the terms of the act under which the works are being constructed; and, by further direction of the President, served as a member of the commission appointed under act of Congress approved June 20, 1878, to select a site for the Naval Observatory, &c.

Colonel Tower has served throughout the year as a member of the Board of Engineers for the permanent improvement of the channel of

entrance to Charleston Harbor, South Carolina, and of the Board of Engineers to take into consideration the improvement of the low-water navigation of the Mississippi and Missouri Rivers, and to submit a plan therefor. He has also served upon the board appointed under act of Congress, approved June 19, 1878, to examine the works in process of construction at the South Pass of the Mississippi River, &c.; as member of board to consider and report upon plan and location for a harbor of refuge at or near Cincinnati, Ohio; of board to consider and report upon project for improvement of the Shrewsbury River, New Jersey; of board for the further improvement of Savannah River and Harbor, Georgia; and of board to consider and report upon the improvement of Pass Cavallo Inlet into Matagorda Bay, and of Aransas Pass and Bay up to Rockport and Corpus Christi, Texas, and also the continuation of the improvement of the entrance to Galveston Harbor, Texas.

Colonel Wright has, under act of Congress approved July 19, 1876, continued to serve upon the commission for the repavement of Pennsylvania avenue, Washington, D. C.; and has served throughout the year as member of the board for improvement of the channel of entrance to Charleston Harbor, South Carolina; and of the board for the improvement of the low-water navigation of the Mississippi and Missouri Rivers. He has also served as member of the Board of Engineers appointed under act of Congress, approved June 19, 1878, to examine the works in process of construction at the South Pass of the Mississippi River, &c.; also, during the temporary absences of the Chief of Engineers during the past year, performing the duties of that officer as acting chief, and other duties assigned to him in that connection.

The Board of Engineers for the Pacific Coast during the past fiscal year has consisted of Lieut. Col. B. S. Alexander, Lieut. Col. C. S. Stewart, Lieut. Col. R. S. Williamson, and Maj. G. H. Mendell, with First Lieut. A. H. Payson recorder, until the death, on the 15th December, 1878, of Lient. Col. B. S. Alexander, since which it has been formed of the other officers above named, with whom Maj. G. L. Gillespie, Corps of Engineers, has, for part of the fiscal year, been associated.

During the year the board has had under consideration the locating of a breakwater and harbor of refuge on the Pacific Coast between the Straits of Fuca and San Francisco, California; also the improvement of Coos Bay, Oregon.

In addition to the above, the members of the board have been in charge of the works of fortification and of harbor and river improvement mentioned elsewhere in this report.

BATTALION OF ENGINEERS AND ENGINEER DEPOT.

Battalion of Engineers, commanded by Maj. H. L. Abbot, Corps of Engineers, headquarters Willets Point, eastern entrance to New York Harbor.

The strength of the Battalion of Engineers on June 30, 1879, was 11 commissioned officers and 192 enlisted men.

It was commanded by Maj. Henry L. Abbot, and was stationed as follows: The headquarters and Companies A, B, and C at Willets Point, New York Harbor; Company E, at West Point, N. Y. Company D is a skeleton organization, at present commanded by the battalion adjutant, and serving on detached duty with troops in the West.

No regular system of recruiting has been carried out during the past year, the vacancies being filled by enlistment and re-enlistments in the

companies and by special assignment from the general depot of the recruiting service, in New York Harbor.

The changes during the year have consisted of 1 death, 50 discharges, 3 desertions, 17 re-enlistments, 30 recruits received, and 3 deserters apprehended, and 2 transfers.

The company at West Point, besides performing ordinary post duties, has aided in the instruction of cadets in field engineering, pontoniering, and military signaling and telegraphy.

The companies at Willets Point have, as heretofore, performed the ordinary garrison duties of the post; cared for, repaired, and issued the property and instruments pertaining to the engineer depot; remodeled a part of the bridge-train to make it conform to the new patterns, and performed needful labor upon the post and public buildings of Willets Point.

The post now constitutes a regular school of application for the engineer service.

The officers are assigned for limited periods to duty with the troops, and thus the whole corps of officers below the grade of field officer, and especially the recent graduates joining from the Military Academy, acquire that experience with enlisted men and that familiarity with company duty which is so essential to a combatant arm of the service.

In addition to these routine duties the younger officers are afforded every facility for acquiring practical experience in the use of instruments and ordinary methods of operation upon the civil works of the country intrusted to the Corps of Engineers.

The tour of duty at Willets Point, which usually follows immediately after the theoretical course at West Point, and covers from two to three years, thus serves the important objects of practical military training of the new officers and of practical instruction in the civil duties to which they are to be transferred as assistants.

In addition to the former military duties of engineer troops in campaign, such as field fortification, pontoniering, sapping and mining, reconnaissance, military map making and printing, and other kindred matters, Congress, since the war, has constituted these troops the Torpedo Corps, for the defense of our coasts against the inroads of hostile fleets.

These new duties are not only of the highest importance, but they also involve much special training, notwithstanding the fact that the familiarity with boats acquired in pontoniering, and with explosives and modes of electrical ignition in land mining, specially prepares engineer troops for the service.

At Willets Point the most systematic attention is devoted to this new branch of warfare, a regular individual training being given to every soldier and full records of his proficiency being preserved.

Officers pass through a complete course of laboratory instructions, designed to render them familiar with all branches of the subject, so far as defensive mines which can be operated from the shore are involved. A fine laboratory, provided with all the needful electrical and other apparatus, has been provided. In fine, everything possible has been done to prepare in peace for the vitally important duty which will cer tainly have to be performed upon the first breaking out of hostilities with any maritime power, the placing of our principal harbors in a defensive state by submarine mines.

Notwithstanding these efforts, it is my duty to invite the attention of the department to the fact that the service is in an unsatisfactory state,