APPLICATION OF THE ELECTKIC TELEGRAPH. 341 



change stations, leaving the transit instrument and clock 

 as before, meeting, however, on one night to observe for 

 personal equation. Fifty stars are then to be exchanged 

 again on not less than three nights, in the new position 

 of the observers, and a new series of observations made 

 for personal equation. 



APPLICATION OF THE ELECTRIC CIRCUIT TO ASTRONOMICAL 

 OBSERVATIONS. 



It is obvious that the electric circuit, as it has been 

 employed in the determination of longitude, may also 

 be employed in the ordinary business of an astronomical 

 observatory. When Professor Locke invented his 

 electro-chronograph, by which the electric circuit was 

 broken, and dots were printed on paper every second 

 by the action of a clock, Mr. Walker and many others 

 anticipated that this would immediately supersede the 

 old method of observing transits of stars. This new 

 method of observation has a great advantage over the 

 old in respect of accuracy. Astronomers have hitherto 

 measured small intervals of time by listening to the 

 beats of a clock or chronometer, and estimating, as well 

 as they were able, the fraction of a second when any 

 event has occurred, such as an occultation of a star, or 

 the transit of a star over the wires of a telescope. The 

 ear is, however, a very imperfect organ. While the eye 

 readily estimates a fraction of a line with the precision 

 of a tenth, the ear seldom distinguishes smaller portions 

 of an interval of time than a fifth. In the opinion of 



