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 pppp 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 wire, which is broken by the ball leaving the gun. The targets Nos. 2 and 3 consist of frames of common deal wood 6 feet square, across which a copper wire passes backwards and forwards close enough to allow no ball to pass through without breaking it. These frames can be raised to such height as the angle of elevation at which the gun is fired renders necessary. The cylinder A has a screw S cut on its axis, which serves as a means of propelling it while the metallic points draw, so that the lines do not fall upon each other, but run spirally round the cylinder with the pitch of the screw. For that purpose the cylinder with clockwork is fixed to a carriage which runs on the wheels while the lever L and the metallic points at p p p p remain stationary. At the further end is a governor to ensure equal velocity of rotation. The apparatus is used in the following manner. A galvanic battery is connected with each of the four electro-magnets; one takes into its circuit the pendulum, the second the target at the muzzle of the gun, the third the target at 100 yards distance, the fourth the target at 200 yards; the pen dulum is then set going, and dots on the cylinder, which is, however, not yet in motion. The clockwork is now set going, and the three points draw lines. After one or two revolutions the command to fire is given, when the ball, in leaving the gun, breaks the wire of No. 1 target, and point No. 1 ceases to draw. When the second target is struck, point No. 2 ceases to draw; and when the third target is struck, point No. 3 ceases to draw. The clockwork is now stopped. To ascertain the time represented by these lines, the paper is taken off; where point one has ceased to draw is the starting point or zero; the length of the second and third lines will give seconds and fractions of seconds, when compared with the distance of the two dots made by the pendulum, for which purpose a scale may be used, or an ingenious contrivance of Mr. Holmes's, a compass to one leg of which a screw is attached with 100 turns, a nut turns in the second leg and subdivides one turn of the screw into 100 parts. By moving the trammels either way the points of the compass can be made to take in the two dots which represent the second, and each turn of the screw will give the 100th part of the second, be the distance great or small. A second cylinder is provided, which may be prepared with metallic paper beforehand so as to save time. Various objections may be raised to this apparatus, to some of which we will briefly allude. Electricians will point out that after the current is broken residue magnetism in the soft iron will retard the release of the keeper. We have provided against this error, firstly, by making the electro-magnets exactly alike, as mentioned before, so that we have the same retardation in the release of the three different keepers, and this error will thus be neutralized ; secondly, by not bringing the keeper into actual contact with the iron, but interposing a thin brass pin. A second objection might be that the different length of the wires might have different, or unequal, effects on the magnets ; if this should be the case, resistance coils might be enclosed in the currents to make them all alike. A third source of error, and perhaps the most inconvenient one, is, that when the three points draw, there is more friction than when they are successively released; but as the amount of friction can be ascertained, it can be allowed for. Only by a great number of reliable observations the theory of projection can be elucidated; and General Anstruther would gladly lend the apparatus to any gentleman desirous of its use, expecting only of him to find his own wire, and to make him (General Anstruther) acquainted with the results.* * The instrument may be inspected at Messrs. Elliott Brothers, 30, Strand, |