5675-78 feet, we may be sure the time of flight is 19.92 seconds, because 19.922 x 14.308 5677.5 feet, only 1.72 feet over, and near enough for our purpose.

39. It only remains to show the initial velocity which would carry a ball from A to B in 19.92 seconds, if not opposed by gravity. As it is seen to do this at 34° 15', clearly it would do so at 45° or any other elevation, the resistance of the atmosphere being the same whatever angle we fire at; the velocity being the same, the distance traversed will be the same if gravity does not act. At any elevation the velocity may, with advantage, be considered as the resultant or equivalent of two velocities, one of them vertical, represented by the sine of the angle of elevation; the other horizontal, represented by the cosine of that angle. To calculate radius, let us suppose sine and cosine equal, that is to say, let us suppose elevation 45°, then the vertical velocity and horizontal velocity each will be represented by v, and their resultant or equivalent, v √2 V, the said V being the real initial velocity of the ball. Dividing A B by the square root of 2, we get the distance 10084 8 = 7131.04 feet, and we see that this is the vertical height to which, if not opposed by gravity, the vertical velocity v would carry the ball in 19.92 seconds.

0.141421356

40. To ascertain what v is, we must see what height a ball must fall from, to acquire by falling such velocity as to pass through 7131-04 feet in the last 19.92 seconds of its fall, and this, though tedious, is not difficult. We find after some few trials that if a ball be suffered to fall by gravity from a height of 7258-8140625 feet it will reach the ground at the end of 22.75 seconds of time, and in the earlier 2.83 seconds of this it will have passed through (2.832 x 16.017 feet) 128.27855112 feet, so that in the remaining 19.92 seconds it would fall through 7130-5355112 AB feet, only 6 inches short of 7131-04, the desired length, or √2

=

The velocity v, which a ball acquires by falling 22.75 seconds, is thus found:

per

41. Then as (V = v √ 2) the initial velocity, resultant or equivalent of two velocities of 586-28649 each, is equal to 586-28649 ✓ 2, it is 829-1343, as we said in para. 38 we should prove it to be.

42. We subjoin a table, C, by which any artillerist may amuse himself by finding the angle of elevation for any time of flight with this velocity, and we shall give three examples of

TABLE A.

Time of Flight 25.5 Seconds. Initial Velocity 636-1385 feet per second.

TABLE C.

Time of Flight 22-75 Seconds. Initial Velocity 586-2865 feet per Second.

AN ELECTRO-CHRONOSCOPE,

Invented by Major-General ANSTRUTHER, C.B.

DESCRIBED BY C. BECKER.

THE object of the electro-chronoscope is to measure exactly the time of flight of a projectile between two given points. Various modes of taking the time of flight have been in use for years. The simplest is a sort of clock, which is divided into 600 parts, and which is traversed by a hand once a minute, and which may be set going and stopped by touching a lever, and from which a second hand may be detached in its course. It indicates to tenths of seconds; but, as the accuracy of this instrument depends upon the manipulation of the observer, it is subject to considerable error. The self-registering principle is therefore the only one which will give reliable results. A beautiful self-registering chronoscope, by Navez of Brussels, is used at present at Woolwich, the results of which are said to be surprising; the only drawback of which is that each observation requires a rather troublesome calculation to reduce it to real time.

General Anstruther had an apparatus designed by Mr. Holmes, which was intrusted to Messrs. Elliott for execution. The principle was in the main the same as represented in the woodcut. A cylinder, covered with paper soaked in a solution of ferrocyanide of potassium, had to revolve driven by a weight. Small iron wheels attached to slight springs had to trace, by decomposition, blue lines on the paper, on the principle of Bain's electric printing telegraph, as long as an electric current passes; but when put into practice it was found that, if we may call it so, a sort of ink was formed which continued to mark after the current was broken, and consequently the object aimed at, extreme accuracy, was lost. In conjunction with Mr. Bashley Britten, C.E., Messrs. Elliott altered the plan. Instead of making use of chemical decomposition by an electric current, they substituted metallic paper for the cylinder A, and a clockwork C for the weight. At a a a a of sketch are 4 electro-magnets made of the same material, in exactly the same manner-a matter of some importance, as we shall presently see. The keepers are attached to springs which carry metallic points p p p p. When the electric current makes the iron magnetic, the keeper is attracted, and the metallic point presses gently on the paper; one of the electromagnets is in connection with an accurately timed seconds pendulum, which at every beat makes connection for a fraction of a second, or, in other words, makes the magnet attract the keeper every second, and dots on the paper cylinder. Thus we have a second registered independently of the velocity with which the cylinder rotates. If the rotation is quicker, the two dots will be further apart; and vice versa. The three other electro-magnets are in electric connection with three targets, one of which is distant about one foot from the muzzle of the gun, the second and third at 100 or 200 yards, or at any other required distance. The first target consists of a simple copper