ASTRONOMICAL USES OF THE TELEGRAPH. 



spacing out the field of view. At night they are rendered visible 

 by a lamp, by which the field of view is faintly illuminated. 



These points being well understood, no difficulty will be found 

 in understanding the manner in which the telegraph has conferred 

 vastly increased facility and precision on such observations. 



269. The first service which it has rendered is that of making 

 all the clocks in the observatory absolutely synchronous. This 

 has been already accomplished with regard to the solar clocks, 

 that is, those which indicate mean or civil time. It may be, and 

 no doubt will be, also accomplished, with still greater advantage 

 to science, in the case of the astronomical clocks, that is, those 

 which mark sidereal time. The several observers, occupied usually 

 in different, rooms, have each their own clock. Now, however 

 perfect may have been the workmanship of these clocks, no two 

 of them can be relied upon to go absolutely together for any 

 length of time ; therefore, one of the duties of the observer, and of 

 the conditions of good observations, is to note the error of his 

 clock that is, its deviation from the standard chronometer of the 

 observatory. These errors will be effaced by the expedient of 

 putting all the clocks in the observatory in electrical connection, 

 so that the pendulum of the standard chronometer shall regulate 

 the pulsations of the current, and these pulsations again regulate 

 the motion of all the other clocks. 



"We believe that the Astronomer Royal once contemplated this 

 improvement, and most probably, when suitable opportunity shall 

 be presented, he will carry it into practical effect. 



270. The clocks being thus reduced to absolute accordance, the 

 next service rendered by the telegraph to the astronomer consists 

 in affording the means of ascertaining the instant of time at which 

 any celestial object passes across the micrometer wires with greater 

 facility and precision than were attainable by the use of the eye 

 and ear in the method above described. 



This improved method of observation, as it is now being pre- 

 pared for the Greenwich Observatory, consists in a key-com- 

 mutator placed under the hand of the observer, which governs a 

 current transmitted to an electro-magnet, connected with a 

 style placed over a cylinder coated with paper, upon which 

 it leaves a puncture when it is driven down by the pulsation 

 imparted to the current by the finger of the observer acting upon 

 the key. The paper-covered cylinder is kept in uniform revolu- 

 tion at any desired rate by clock-work, and another style impelled 

 by another current receiving its pulsations from the pendulum 

 of the chronometer, is driven upon the paper with each beat of 

 the pendulum, the interval between two successive marks made 

 by this style representing one second of time. 



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