ing down some of the other sheds that are no longer needed, and other necessary repairs to the depot buildings have been made.

VII. An additional derrick was erected on the long wharf, to give ad ditional facilities for handling torpedo materials.

DEPOT PROPERTY.

The surveying, astronomical, and other instruments in the depot have been properly cared for, and the following additions have been made during the year by purchase, viz:

Two sextants, 4 transits, 2 engineer levels, 11 metallic tapes, 10 steel tapes, 5 binocular field glasses, 10 steel chains, 8 leveling rods, 5 hand levels.

The following instruments have been received in depot from officers on public works, viz:

Eight theodolites, 3 engineer levels, 1 plane table, 2 gradienters, 1 astronomical transit, 10 prismatic compasses, 6 odometers, 1 barometer aneroid, 3 sets drawing instruments, 3 pocket compasses, 1 sextant, 3 steel chains.

The following instruments have been transferred to officers of the corps and to acting engineer officers on public works, viz:

Six engineer levels, 3 sextants, 1 gradienter, 1 plane-table, 4 current meters, 2 odometers, 6 theodolites, 1 standard yard, 2 surveyor's compasses, 11 hand levels, 9 pocket compassess, 3 Abbot's protractors, 1 boat compass, 5 level rods, 6 aneroid barometers, 7 thermometers, 4 steel chains, 13 prismatic compasses, 2 sets of pins, 2 metallic rulers, 1 metallic triangle, 6 metallic tapes, 4 steel tapes, 3 binocular field glasses, 2 sounder instruments, 1 circular protractor, 2 sets drawing instruments.

Most of the repairing of the instruments during the year has been done by detailed enlisted men of the battalion, and the cost has been very much less than it would have been if the instruments had been sent out to private shops, while the character of the work done has been satisfactory.

The following instruments have been overhauled, cleaned, and put in good order during the year, viz:

Sixteen prismatic compasses, 2 engineer levels, 1 standard yard, 1 plane-table, 4 steel scales, 1 gradienter, 2 current meters, 2 transits, 3 steel chains, 1 sextant, 2 steel tapes, 3 theodolites, 2 engineer levels, 1 hand level, and a number of smaller instruments, and minor repairs on instruments not mentioned above.

Electrical test instruments have been also repaired in the depot repair shop to advantage, but such instruments as could not be repaired here were sent to private shops, and the expense during the fiscal year including bills paid for repair of instruments at distant places, paid in accordance with instructions from the Chief of Engineers, amounted to $165.80.

As no electrical instruments have been bought for several years, during which time many new and improved forms have been devised, it was found necessary to purchase quite a number of these instruments for use in the laboratory as well as to illustrate the progress now mak ing in these matters both in this country and in Europe. Some of these instruments have been received and others are daily expected. Among these instruments are ammeters and voltmeters of some of the most approved paterns, adapted to all measurements likely to be required.

EXPERIMENTS.

The appropriation for continuation of torpedo experiments was not available until November 5, 1888, and, as explained in former reports, there had been no appropriation for this purpose for the two preceding

fears, so that all the experiments that could be attempted were such as could be made with the materials on hand or that could be improvised without much expense. During this time we were also greatly crippled, both in making experiments and in the instruction of soldiers in planting and operating torpedoes, by the failure of the steam-launch and the propeller Bushnell, both of which gave out last fall and could not be made ready for this season's work. By borrowing a steam-launch from the Navy Department, the difficulty has been, in a measure, overcome, and it is hoped the Bushnell will soon be in use again, but the other boat will not be worth repairing and can only be used as a raft for carrying materials.

I. Tests of explosives.-The apparatus for testing high explosives was repaired and other preparations were made early in the spring for such tests as might appear desirable, and samples of emmensite were ordered for trial, but an accidental explosion occurred at Dr. Emmens' works just as he was ready to ship the explosive, destroying the works as well as the samples, and he has not been able to replace them. He states, however, that he expects to be able to furnish some of his powder at an early day, and it will be tested as soon as received.

Samples of roburite were also promised, but have not been received. In this connection it may be proper to state that, although the number of different explosives has nearly reached three hundred and fifty, none have been discovered which give any great promise of superseding gun-cotton and dynamite for sea mines; and for all purposes, both mili tary and industrial, only a very limited number of the so-called inventions will probably ever be brought into general use.

II. Crater gauge.-Some additional experiments were made with the crater guage, and it was intended to take it into deep water, but owing to the breaking down of the Bushnell this could not be conveniently done, but will be tried later.

In addition to the conclusions given in my last report, it has been found, or, at all events, "the indications are":

1. That for each charge there is a depth at which the crater will be spheroidal in form, while at greater or less depths it will be "pear shaped," the smaller end being downward for less depths, and upward for greater depths.

2. The surface (not the volume) of the crater appears to vary about with the weight of the charge, the latter being of musket powder.

3. It makes but little difference whether the slides are set close to the ring at the center, or at considerable distance, provided, of course, they are inside the limits of the crater due to the given charge.

Four additional wires and slides were inserted near the vertical wire in order to get a more accurate record of what takes place in that direction.

It should be explained that the apparatus in question consisted of a wooden frame 15 by 20 inches square, with radial wires running from a thin iron ring at the center, the whole figure being something like a spider's web, with wooden slides on the wires so arranged as to be of the same density as water, and to leave a small rubber washer at the extreme point, to which they are carried by the explosion. The charge (which is necessarily small, from 1 to 5 pounds) is placed in the center of the ring, and the whole frame is lowered vertically into the water to the desired depth just before firing. Plate I shows some additional results obtained with this apparatus.

III. Pressure gauge.-Another apparatus for accurate measurement of small pressures, such as would result from the explosion of a small

charge, or from a large one at considerable distance, is shown on Plate II. It consists of a compressible cushion to receive the pressure and a steamgauge to register it, these parts being connected by an iron pipe of suitable length, and having an attachment for a bellows or air-pump. If this cushion be placed at the desired depth and distance from the charge to be fired, it is evident that any compression of the water would compress the air in the cushion, and cause a sudden rise in the index of the gauge. This, however, would give a ballistic effect instead of a statical one, and to avoid this difficulty it is necessary to compress the air in the cushion and gauge to about the pressure expected from the explosion. If the pressure from the explosion does. not exceed this assumed pressure, no perceptible rise will be observed in the index, but if a rise is noted it will give a good idea of the proper pressure at which the gauge should be set for the next explosion. The results obtained show that this is by far the most accurate method yet devised for measuring small pressures, and the facility with which it may be used renders it a very convenient instrument for investigating the effect of explosions at considerable distances and the law governing such effects.

It has been found that a charge of 10 pounds of mortar powder, 10 feet below the surface and 10 feet horizontally from the gauge, will not give a pressure of more than 10 pounds per square inch. Arrangements are nearly perfected for giving this method a thorough trial, and the results will be reported later.

IV. Torpedo drill.-Five grand groups of torpedoes were planted during the season by different detachments of officers and men. When a group has been planted and tested, its position is located on the chart and a tracking drill with search lights is ordered. The officers are required to superintend all the details of the instruments, dynamo, and projectors. A steam-launch is followed in various directions through and across the group, and a small charge of dynamite is fired whenever she is judged to be dangerously near the torpedo which it represents. The fuses in the torpedoes are also fired, and a record made of the fact when a torpedo is taken up.

The object of this drill is twofold; it accustoms the officers and men to the duty of handling, planting, and operating the system, and it furnishes reliable data for correcting defects in the system and in the methods of using it.

The Mangin projector, ordered several months ago from Messrs. Sautter, Lemmonier & Co., of Paris, has been delayed much longer than it should have been, but the makers now promise to send it at once, and it will be set up and tested as soon as it arrives.

V. Range finders and position indicators.-One of the most important instruments yet to be invented is a quick, simple, and reliable instru ment for determining the distance of moving objects. Several of the young officers have been set to study this problem, and a number of dif ferent instruments for the purpose have been tested and studied, but nothing satisfactory has been found. It is proposed to continue the investigations, however, and one or two new instruments will be constructed in the near future.

VI. Several photographs of explosions in air and water have been made, but they are not yet satisfactory, and it is hoped that better ones may be taken. Some of those taken by Lieutenant Hale and Sergeant Von Sothen, six in number, marked IV to IV, inclusive, are forwarded herewith. In some cases powdered magnesium was used to increase the actinic effect, but with ordinary powder the flame is distinctly visi

ble. The charge used, and other circumstances under which the pictures were taken have been noted on each photograph.

VII. In order to ascertain whether some parts of the system could be improved, a Board of officers was convened to examine into the subject and report on the advisability of further experiments in connection with mooring rope, shackles, cut-off boxes, torpedo cases, etc.

A copy of the order, instructions, and reports of the Board is forwarded herewith, marked D. It is not, however, in a condition for definite action, being merely a preliminary step, and it is forwarded to show the line of investigation it is proposed to follow. The papers will, however, explain themselves.

VIII. A number of specimens of building stone have been tested at the request of officers engaged on river and harbor works. Lieutenant Reese has attended to this duty, and has obtained very satisfactory results, considering the facilities at hand.

A "Jolly" spring balance for specific gravity has been procured, and it is proposed to try some experiments on the ratio of absorption under high pressures.

ALyman" wave-model has also been procured for illustrating the subject of wave-action.

IX. Some tests of service fuzes and of a new form of "machine-made” fuzes have been made. Some of the results are shown in Appendix E. One anomalous result observed was that some of the fuzes that had been on hand for several years gave a lower resistance when heated than when cold. On opening these fuzes globules of free mercury were found, apparently formed by the decomposition of the mercuric fulminate, though I have never seen it stated that such a decomposition is possible. The machine-made fuzes gave remarkably uniform results, and some suggestions were given for improving them in other respects, but the new lot has not been received.

X. Sims Torpedo.-As there is an allotment of $5,000 for buying motors for some of the torpedoes furnished by Mr. Sims several years ago, and as he now claims to have made great improvements in his motor, a number of trials of this torpedo were made and others are proposed.

The new motor is adapted to a much higher speed than the old one, and the current required to drive it has a much higher E. M. F., in some cases reaching 1,300 volts. To provide for this the cable is much better insulated than the old ones, the wire being very fine and the dielectric being nearly pure rubber put on in strips wound round and round. It is then passed through melted paraffine and coated with dry cotton and finally with a braid of tarred hemp. The insulation seems to be excellent, and no instance of a leak in it has occurred, notwithstanding the high voltage and the fact that it has been wound and unwound ten or twelve times. It is doubtful whether this insulation would last long in store unless it was constantly submerged in water. The torpedo carries about one mile of this cable, but it is very little larger than the old cable.

The torpedo itself is smaller and the float is longer than the old one, while the model is intended to be better adapted to high speed. Plate III shows the form and dimensions of the torpedo complete.

The motor is geared to make two revolutions to one of the propeller, which is 30 inches in diameter and 30 inches pitch. A propeller with 36 inches pitch was tried in one run, but failed to give the speed attained with the 30-inch pitch.

The results of the trials with this torpedo show that it can far exceed ENG 89-31

any results heretofore attained with it, the best speed with the old motor being about 10 miles per hour, while the new one gives over 18 miles.

After a preliminary dock-trial, the following runs were had for speed, viz:

June 3, 1889.-The torpedo started all right, but at moderate speed, and soon showed signs of a "short circuit." Steered to the left, and stopped at about 500 feet. On opening the torpedo, the coupling between the cable and the motor sections was found burned out. This was evidently caused by a slight leakage along the cotton cover of the cable which had not been removed.

June 7, 1889.-The steering gear failed to work. Three starts were made, and she appeared to travel considerably faster than the old boats, but could not be guided, and failed to pass the second stake-boat. The rudder post was found to be considerably bent.

June 10, 1889.-The forward part of the rudder having been consid erably reduced, a run of about 900 feet was made. The speed was good, and the steering successful, but one of the belts of the dynamo broke and the run was stopped. This was one of the old V-shaped belts, and the result showed that they were not strong enough to drive the large dynamo. They were at once replaced by a 12-inch flat belt, with larger pulleys, and it is not expected that any more trouble will arise from that source.

June 19, 1889.-The first successful run was had. The torpedo seemed to be under control, and made the distance of 2,510 feet in 110.2 seconds, giving a speed of 15.5 statute miles per hour. The course was marked by buoys and a flag was dropped at the instant the torpedo passed each buoy, the time being marked by a chronometer and a Morse register. The torpedo was also tracked and plotted by a party of officers under Lieutenant Wilson, but the transits worked badly and the results were submitted as approximate only. The run was at 3.30 p. m., an hour before high tide.

June 21, 1889.-Another ruu was made over the course, a third buoy having been placed 805 feet beyond the first, and 1,705 feet from the third buoy. The run was at 11.30 a. m., about one hour before low water. Time from first to third buoy 101 seconds, the distance being 2,510 feet and the speed 16.96 statute miles. From the second to the third buoy the speed was 17.4 statute miles per hour. The propeller turned with difficulty, and it was roughly estimated that about 5 horsepower would be wasted in friction. On the recovery of the boat it was found that the shaft turned still harder, and an examination showed that the bearings had become heated and required readjustment.

June 27, 1889.-The run was set for 10.30 a. m., but owing to certain breaks in the circuit it did not come off till 12 m., an hour and a half after high tide. The time was marked by Captain Roessler, on a Morse register, and by Lieutenant Wilson with a stop-watch. Lieutenant Lucas read Thomson's electrostatic voltmeter, and Sergeant Newman the Ayrton & Perry am-meter, No. 1067. Speed of the dynamo was taken by Lieutenant Taggart, and Sergeant Kennedy read Mr. Sims' voltmeter. The run was a good one, the time of the passage between the first and third buoys, by Captain Roessler and Lieutenant Wilson, being 98.4 seconds, giving an average speed of 17.4 miles per hour. Between the second and third buoys the speed was 18.2 statute miles per hour. The potential at the dynamo varied from 1,160 to 1,260 volts, and the current was from 34.5 to 38.5 amperes. Highest dynamo revolutions, 1,040 per minute.