APPLICATION OP THE ELECTRIC TELEGRAPH. 329 



Mr. Kerrison has invented a method of regulating the 

 motion of the registering cylinders by means of two 

 short pendulums attached to cranks, in such a manner,- 

 that the one crank shall be at its maximum effect when 

 the other is passing its dead point. The weight, by 

 which the works are kept in motion, has in this arrange- 

 ment a considerable influence on the velocity ; conse- 

 quently it was found very difficult to regulate it, and 

 when regulated, almost impossible to keep it so. The 

 number of pendulums were increased by Mr. Kerrison in 

 the hope of overcoming the difficulty, but hitherto 

 without success. 



Professor Mitchell's method of recording right ascen- 

 sions was invented in 1849, and consists of a horizontal 

 disc which is made to revolve with uniform velocity once 

 a minute on a vertical axis. This disc carries either a 

 metal plate, or a paper disc, on which the time and ob- 

 servations are recorded by pens drawn by electro-mag- 

 nets. At every alternate second, a dot is struck by the 

 time-pen on the paper. When the disc has performed 

 one revolution, a tooth upon the axis of the disc takes 

 hold of a fixed rack, and moves the traveling frame, 

 which carries the center of the disc through the tenth 

 of an inch, when a new circumference of time dots is 

 commenced. The observation dots fall intermediate 

 between the minute circles and second dots, and are struck 

 so as to distinguish them by form from the time dots. 



