Schultz By means of this instrument, designed for the measurements of very short intervals of time, periods varying from 30 seconds to the one five-thousandth part of a second have been measured with very great approximation, and with great ease and accuracy. It was introduced into the United States for the purpose of determining the initial velocity of projectiles in the proof of gunpowder. A tuning fork, caused to vibrate by electromagnets, makes an ascertained number of vibrations per second; it traces on the surface of a revolving cylinder a sinuous line showing the beginning and end of each vibration. This sinuous trace is an actual scale of. time. The instant at which a projec tile reaches any point in its trajectory is by the application of electricity marked upon the cylinder beside the scale of time. The number of vibrations comprehended between any two consecutive marks .is an exact measure ment of the time elapsing between the instants at which the projectile occupied the corre sponding positions in its trajectory. The meas urement of time depends on the equality of duration of the vibrations made by the fork; the number of these vibrations in the unit of time is fixed by the construction of the fork. The principal parts of the machine are the cylinder vibrating fork, electromagnets, the wheel-work, the electric interrupter, Rhumkorff coil, pendulum and micrometer, and, while ex perimenting the. galvanic batteries and targets. The cylinder has a double motion of rotation against the tuning fork on the inner side of the prong, making the fork its own interrupter when the electrical current is passed through it.
Hipp Chronoscope.— In this instrument a falling weight sets in motion a clock-work which is regulated by a rapidly vibrating spring. Electromagnets make this clock-work engage and disengage a registering dial. The instrument reads in thousandths of a second.
Benson's chronograph is, in principle, a lever watch with double seconds hands, the one superimposed on the other. The outer end of the lowermost hand has a small cup filled with a black viscid fluid, with a minute hole at the bottom, while the corresponding end of the uppermost is bent down so as just to reach the hole. When in operation a string is pulled, and translation, given by means of a weight acting on a system of clock-work The silvered face of the cylinder is covered with a thin coating of lamp-black, which is removed by the trace and spark, exposing the surface in strong contrast to the blackened parts. The
vibrating fork stands immediately in front of the cylinder; on each side of it is an electro magnet to originate, sustain and equalize the amplitude of the vibrations. The left branch of the fork is armed with a flexible quill-point, which, by an eccentric roller, can be made to touch the cylinder at pleasure and thus make the traces upon it. The interrupter is the mechanism by which the current for the fork's electro-magnets is made and broken. In the Schultz Chronoscope at West Point the de tached mercury interrupter has been replaced by a light metallic spring, which is pressed whereupon the bent end of the upper hand passes through the hole and makes a black mark on the dial, instantly rebounding. This chrono graph, which is sometimes called a stop-watch or a split-second fly-back watch, registers to one-tenth of a second.
Very ingenious devices are employed for special kinds of work. Thus for registering the exact times of the ((transit" of a moving star across several wires in the field of the telescope, a moving wire is sometimes kept ac curately upon the star's image (either wholly by hand or partly driven by a small motor) and at the instant when the moving wire reaches the position of one of the fixed wires the current is automatically closed and the record made. In another device for the.same purpose the clock each second untovers4 delicate photo graphic plate placed at focus of the tele scope; the plate' when developed thus shows a series of dots which are the positions of the star at successive seconds. The wires of the instrument are also photographed upon the same plate directly. In this form the plate itself becomes the astronomical chronograph. It should also be mentioned that in a very ingenious form of chronograph invented by this time the insect eats no food, living upon the fat stored up by the larva. (See PUPA). The chrysalides of butterflies differ from the pupae of moths in being often ornamented with brilliant golden spots which have given origin to the name 'chrysalis" or "aurelia, Also the body is often. strengthened or protected by tubercles situated on the head, back and sides.
G. W. Hon* the closure of the key by the observer records upon a moving tape the exact time to one-hundredth of a second when the closure was made, the figures expressing the hours, minutes and seconds being directly printed upon the paper. This does away with the necessity for a later measurement of the chronographic record, for the figures can be readily read from it.