170 Velocity of t?u Electric Current. 



3. The olook could he made to open and close the circuit, at either 



end of the line. 



4. Bach relay could record the clock heats OD the chruiioyraidi. 



5. Eaoh relay could work a local .-minder. 



For accomplishing these changes, ten movable switches 

 wore necessary. 



Chro?iogra]>/t. 



The chronograph used in these experiments is a revolv- 

 ing disk, provided with two recording pens, worked on 

 an open circuit. It is capable of recording time to the one- 

 thousandth part of a second, and has been fully described 

 in vol. i, Annals of Dudley Observatory. 



The local circuit passing through the sidereal clock, 

 included chronograph pen, No. 1, together with a small 

 pony sounder, arranged to close the main line circuit in the 

 same manner as an ordinary relay. When the clock was 

 thrown in circuit its beats were recorded on the chronograph, 

 by pen No. 1. As the sounder worked simultaneously with 

 the chronograph pen, the main circuit would necessarily be 

 opened and closed at the same instant, and the rcla}'s would 

 be operated. If then the necessary connections were made, 

 the relay would record the clock beats on the chronograph 

 with pen No. 2. Now in case the length of the main line 

 was only a few miles, and the armature time of the mag- 

 nets zero, the two chronograph pens would record tho 

 clock beats simultaneously. This condition can be se- 

 cured, by increasing the armature time of pen No. 1, so 

 that it shall equal the sum of the armature times of the 

 pony sounder, relay, and pen No. 2. We have, however, 

 thought it preferable to reduce all the armature times to a 

 minimum, and determine it for each separate magnet. 



