CHRO NOGRAPH. Different forms of time-measures, or time-recorders, under this designation, have been invented within a recent period.
Benson's chronograph is intended to int:a:tire intervals of time down to tenths of a second, for use at horse-races and other occasions where a seconds watch is not exactly suited. It has an ordinary quick train-lever movement, carrying hands which move. over a dial. One of these is a seconds hand, very peculiarly made. The seconds hand is double, consisting of two distinct hands, one superposed on the other. The outer end of the lowermost hand has a small cup with a minute hole at the bottom; while the corresponding end of the uppermost hand is bent over so as exactly to reach this punc ture. The little cup is filled with ink, having a consistency between that of writing fluid and printers' ink. Suppose that a horse-race is about to take place. The observer keeps a steady look-out for the fall of the starter's flag, or whatever the signal may be: he gives a pull to a cord or string connected with the mechanism peculiar to the instru ment; by this movement, the outer and bent end of the upper seconds hand dips down through the ink-cup iu the lower hand, and through the puncture to the dial. A small black spot or mark is thus made upon the dial-plate; and this is repeated as each horse passes the winning-post. If the eye and hand of the operator are quick and accurate, there is a reliable record thus presented by the instrument of the duration of the race, sometimes as close as one tenth of a second. The instrument is now adopted at the principal races as a suitable one for the purpose; thus it is used for races such as the Derby, the Oaks, the Goodwood, the St. Leger, etc. It is also available for many other
purposes.
Strange's chronograph is designed fora more scientific purpose, and constructed with more careful details. The object is to measure extremely short intervals of time, for the determination of longitudes in great trigonometrical surveys. The observer, when a particular star traverses the field of his telescope, touches a small ivory key; and on the instant, a dot or mark appears on a sheet of paper coiled round a barrel. The instrument being connected with an astronomical clock, there is a dot made for every beat of the pendulum; and as these dots are a considerable space apart (consider able, that is, for the refined instruments of the present day), it is possible to determine so wonderfully minute an interval as one hundredth of a second.
Other forms of chronograph have been adopted by astronomers. One was sug gested by prof. C. A. Young in 1866 to assume the functions of a recording chrono graph, by marking the instant of observation in hours, minutes, seconds, and hundredths of a second, in printed characters, and in a form suitable for preservation and reduction.
Chronographs connected with electric and magnetic apparatus are used for determin ing the velocity of projectiles. Many forms have been devised by Noble, Bashforth, Navez, Le Bouleuge, and other inventors. The most general arrangement consists in causing the bullet to pass through a series of screens; the rupture of each screen breaks for a moment the continuity of an electric current, sets in action an electro- magnetic apparatus, and makes a permanent mark or record.