Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/314

298 G U N N E li Y sever a fine wire stretched across a screen, thus breaking an electric current, and causing a record to be made by the FIG. 1. Bashforth Chronograph, instrument at the moment. The Le Boulenge" is connected with two wire screens only, the others with several. As two records are necessary to obtain a velocity, reading the time taken by the shot to pass between two screens, the number of points of a shot s flight at which an instrument is capable of indicating the velocity is one less than the number of screens employed. The chronograph invented by the Rev. F. Bashforth, late professor of mathematics to the Advanced Class of the Royal Artillery, is shown in fig. 1. A is a fly-whed, which, in revolving, carries with it K, a cylinder Bashfoi covered with paper specially prepared to receive the records of the chrono- clock and screen. B is a toothed wheel which turns the drum M graph, and unwinds the string CD, thus allowing the platform S to descend slowly down the slide L. E, E are two electromagnets, whose keepers are supported by the frames d, d ; f, f are the ends of springs which act against the attraction of the electromagnets. There are two distinct currents one through the screens and E, the other through the clock and E . When these are interrupted, one by the shot cutting a screen, or the other by the clock beating seconds, so that the magnetism is destroyed, the spring/ or/ carries back its keeper, which, by means of the arm a or a , gives a blow to the lever b or b , causing the marker m or m to depart from the uniform spiral it has been describing a spiral consisting of a double line running round the cylinder. The apparatus is adjusted so that the platform L, and consequently the markers m, m , descend about inch for each revolution of the cylinder ; the folds of the spiral are thus | inch apart. The cylinder is made to revolve with considerable rapidity, so that the intervals between the successive clock marks indicating seconds measure from 20 to 25 inches ; hence the screen marks indicating the moment of the severance of the wire by the shot can be allotted to their proper value in seconds with great accuracy. The screens are so contrived that the current, interrupted by the passage of the shot through one, is completed again before the next is reached. To accomplish this, the cutting of the wire is made to release a spring which makes a fresh contact ; thus any number of screens can be used and a corresponding number of records obtained. The chronoscope invented by Captain Noble of Elswick, Noble late Royal Artillery (figs. 2, 3, 4), is constructed to furnish chrono eight or more records, according to the number of discs, sc P e< and is so excellently adapted for the measurement of exceed ingly minute portions of time that it is usually employed to ascertain the velocity acquired by the shot in moving from a state of rest inside the gun at different parts of the bore. It is thus intimately connected with gunnmking, INSTRUMENT ABOUT ^ r ." GUN ABOUT

FIGS. 2, 3, 4. Noble Chronoscope.