122 ANNUAL OF SCIENTIFIC DISCOVERY. 



an ingenious arrangement of the machinery, the end of each minute, of 

 each five minutes, and of each hour, is represented, so that the exact 

 period when an observation is made may be determined without counting 

 the seconds. The beginning of a minute is recorded by the omission 

 of a break between two seconds, when the confluent lines extend, say 

 an inch. The commencement of an hour is indicated by a line of 

 double the length of the five-minute line. 



The remaining* part of this chronograph is the break-circuit key, by 

 which the period when an observation is made is determined. The 

 astronomer at any station on a line of several thousand miles in length, 

 may imprint on the register the date of any event by simply tapping, 

 after the manner of playing upon a piano, upon a break-circuit key. 

 This imprints in the indented line a corresponding break-circuit space. 

 Two or three spaces may be printed in one second, if desired. Two 

 seconds of time is ample for the equatorial interval of the wires of a 

 transit instrument. The net-work of spider lines is divided into some 

 nine or more tallies, or distinct groups of five wires each. All these 

 tallies in the case of the transit of a star are imprinted on the register, 

 in the time occupied by the ordinary method for a single tally, to 

 which a transit has been usually limited. The skill required for tap- 

 ping on the key at the instant of the bisection of a star is easily ac- 

 quired, and the accuracy of each imprint is much greater than that of a 

 single record by the common method. The imprints furnish a per- 

 petual record of the date of the event, and may be read off with great 

 rapidity to the hundredth of a second, by means of a graduated scale 

 of the paper used for registering. 



Those who understand the general principles of the magnetic tele- 

 graph will readily comprehend the main principles of this invention. 

 The value of it can only be estimated by the astronomer. In deter- 

 mining longitude, the observations of many nights, even for years, 

 have heretofore been necessary in order to secure accuracy. With 

 one of the clocks of Dr. Locke, the difference of longitude between 

 the National Observatory at Washington and any other point reached 

 by magnetic telegraph may be determined in one night so closely as 

 to show in what part of the building the observations were made. 



Lieut. Maury, in a letter to the Navy Department, after describing 

 the instrument, says : "Its powers are such that the astronomer in 

 New Orleans, St. Louis, Boston, and every other place to which 

 the magnetic telegraph reaches, may make his observations, and at 

 the same moment cause this clock, here in Washington, to record the 

 instant with wonderful precision. Thus, the astronomer in Boston 

 observes the transit of a star as it flits through the field of his instru- 

 ment and crosses the meridian of that place. Instead of looking at 

 a clock before him, and noting the time in the usual way, he touches 

 a key, and the clock here subdivides his seconds to the minutest frac- 

 tion, and records the time with unerring accuracy. The astronomer 

 in Washington waits for the same star to cross his meridian, and, as 

 it does, Dr. Locke's magnetic clock is again touched ; it divides the 

 seconds and records the time for him with equal precision. The dif- 

 ference between these two times is the longitude of Boston from the 



