NATTKAL PHILOSOPHV. 121 



DR. LOCKERS ELECTRO-CHRONOGRAPH. 



IT is well known that Congress at its last session appropriated 

 $10,000 to be paid to Dr. Locke for one of his electro-chronographs, 

 to be erected by him at the National Observatory in Washington. 

 This instrument has now been finished in Boston and forwarded to its 

 destination. Much curiosity has been excited in regard to this impor- 

 tant invention, and we have compiled from a great variety of sources a 

 description, which it is hoped will serve to convey some idea of the 

 working and purpose of the electro-chronograph. 



The object of this instrument is for the determination of the exact 

 period, to the hundredth or even the thousandth part of a second, of a 

 transit or other astronomical observation by which longitude may be 

 ascertained. The difference of longitude of any two places, it is well 

 known, is determined by observing the period of the occurrence of 

 certain celestial phenomena, such as eclipses, transits, occupations, 

 &c. In order to insure perfect accuracy, the utmost exactitude in 

 regard to time, even to the fractional part of a second, is desirable. 

 The usual practice has heretofore been for the observer to note the 

 exact time of the transit or other phenomena by listening to the beats 

 of a clock or chronometer, and estimating the fraction of a second be- 

 tween two beats when the event occurs. This requires a nicety of 

 hearing only attained by long practice, and when attained, still far 

 from being a perfect measure of time. By the invention of Dr. Locke, 

 the observer can record the exact time on a fillet of paper, without 

 taking his eye from the telescope. 



The instrument of Dr. Locke, which he has termed an Electro- 

 Chronograph, is a combination of the magnetic clock, Morse's tele- 

 graphic register, and a break-circuit key, or instrument for interrupt- 

 ing the magnetic circuit. The first, or magnetic clock, was invented in 

 England, by Mr. Wheatstone, about the year 1841. An invention 

 of a similar character was also made by Mr. Bond of the Observatory 

 at Cambridge. Its object is to make several clocks on the same tele- 

 graph line, even at a distance of hundreds of miles, mark the same 

 instant of time. This is done by breaking the circuit of the magnet- 

 ic fluid at each second of time. The method of interrupting the cir- 

 cuit in the clock of Dr. Locke is different from that adopted by 

 Wheatstone, and has this advantage that it cannot alter the rate of 

 the most delicate astronomical clock. With this clock is combined a 

 register, by which, instead of the beats of the clock at one extremity 

 of the telegraph line being made audible only, as was contemplated 

 by Wheatstone, they are made xisible as well as audible, by being 

 imprinted on a fillet of paper which revolves around a drum. In the 

 Morse register, when the magnetic circuit is unbroken, a continuous 

 line is made. 



The magnetic clock of Dr. Locke interrupts the circuit at each 

 second, and produces breaks which represent the second on the fillet of 

 paper at the other end of the line. The dashes or lines between each 

 break are exactly of a length, and each break represents a second. By 



11 



