piece of white paper and mixing it thoroughly, globules of mercury could be distinguished in every case without the aid of a lens, and with the lens numerous small globules could also be seen. Fuzes 1, 14, 16, 17, 33, and 38, all having a high resistance cold diminished in resistance when heated. The resistance in each case seemed to vary, increasing and decreasing, but principally decreasing, until the fuze exploded. These fuzes belong to one of these two batches, Sergeant Kelly is unable to tell which:

December 1, 1879, Goodyear 5,000 platinum fuzes (service cut off), at 6 cents. Between 1880 and 1886, Goodyear 5,150 platinum fuzes (wooden), at 6 cents.

They were issued by Sergeant Kelly to Sergeant Seymour about two weeks ago.

WILLETS POINT, NEW YORK HARBOR, April 18, 1889.

SIR: The following are the results of the tests of three sample lots of fuzes furnished by H. Julius Smith, Pompton, N. J. The fuzes were identical in construction and differed only in the amount of the priming charge:

First sample, 6 fuzes, contained 1 grain fulminate of mercury.
Second sample, 6 fuzes, contained 2 grains fulminate of mercury.
Third sample, 6 fuzes, contained 4 grains fulminate of mercury.

The construction of the fuze is briefly as follows: The fuze wires are of the same length, 7 inches long, and consist of No. 22 B. W. G. copper wire, insulated with a single wrapping of cotton, impregnated with a preparation of coal tar. They are held together in the fuze by a double metal clamp, inch in width and inch long, having two parallel grooves in which the wires are clamped. The bridge end of the wires project about inch beyond the clamp. The clamp is imbedded in a sulphur composition contained in a thin paper cylinder, inch in exterior diameter and a little over 1 inch long. The bridge wire, which was furnished by the engineer depot at Willets Point, was the standard platinum wire, .0025 inch in diameter. As specified in the order to Mr. Smith, the length of the bridge was to be inch. The upper end of the fuze case or cylinder was closed by sulphur composition. The paper cylinder was covered by a black water-proof composition.

The resistances of the fuzes cold, and at the instant at explosion, and the currents required to explode, are given in the following table:

.53

Ohms. Ohms. Ohms. Ohms. Ohms. Ohms. Amperes. Amperes. Amperes.

.49

.70

61

.55

3

.57

.52

.67

4

5

.57

55

52

6

.53

.55

The grand mean of resistance cold is .58 ohms. The grand mean of resistance hot is .72 ohms. The grand mean of current at explosion is .54 amperes.

The corresponding figures for the fuze heretofore used are given on page 81 of the manual, as follows: Resistance, cold, .7 ohms; resistance hot, .8 ohms; current at explosión, .48 amperes.

It is thus seen that the resistances of Mr. Smith's fuzes, both cold and hoth, are less than those of the fuzes heretofore used, and the currents required to explode are greater. If the bridge wire was adjusted to the proper length I can find no satisfactory explanation for the former. The greater current for explosion may perhaps be due to a greater heat conductivity in the parts surrounding the bridge wire, whereby the heat is more rapidly conducted away and a correspondingly stronger carrent is required to bring the bridge to the proper temperature.

The amount of charge, as well as could be judged by the violence of the explosion, was uniform for each day. The upper part of the paper case is the only part demolished by the explosion, the lower half, that containing the clamp, remaining practically intact, even with the four-grain fuze, in this respect differing materially from the wooden plug fuze which is shattered into small fragments. The ends of the wires holding the bridge are bent outward, and in one instance where the fuze was contained in a piece of core-joint tubing, and exploded in a chamber of a mine switch, one of the wires nearly perforated the tubing, thus showing that there was some danger of contact being made in this way between the wire and the side of the chamber. It was thought that there was danger of the insulation of the wires where they enter the metal clamp becoming injured by the explosion, thus making a short circuit between wires and clamp, but no weakness of this character was developed. The following alterations in the samples are suggested:

(1) That the wires, where they project beyond the clamp to form the bridge, be made as short as possible, shorter than they were in the sample, so that when they are bent outward by the force of the explosion there will be less danger of a short circuit by their being driven through the rubber tube and against the wall of the chamber.

(2) That a braided insulation, or at least a double wrapping of cotton, be used to insulate the wires, the single wrapping being liable to open at any point and expose the bare copper. This defect in the sample submitted was brought out in an attempt to load a few of the fuzes in the mine switch to be fired under service conditions.

Very respectfully, '

The POST ADJUTANT.

S. W. ROESSLER,
Captain of Engineers.

PRESSURE GAUGE
-for-

Submarins Explosions.
W.R.KING

LX. Col. En $15.

tws.