APPLICATION OF THE ELECTRIC TELEGRAPH. 347 



tooth is dropping upon its bearing ; so that the resistance 

 of the springs does not affect the legitimate action of the 

 train upon the pendulum. 



The other pricker is driven by a galvanic magnet, 

 whose circuit is completed by an arbitrary touch made 

 by an observer's finger upon a contact piece. There are 

 three contact pieces. One is upon the eye end of the 

 transit circle ; the other two are upon the base plate of 

 the altazimuth, one to be used *with vertical face to the 

 right, the other with vertical face to the left. Thus alt- 

 azimuth observations are referred absolutely to the same 

 time record as transit circle observations. 



It is necessary to mark upon the revolving barrel the 

 beginnings of some minutes ; and the numeration of some 

 hours and minutes. This is done by arbitrary punctures, 

 given by the observer's touch. In order to guide the eye 

 through the multitude of dots upon the sheet, lines of ink 

 are traced by means of a glass pen, which is attached 

 to the same frame as that by which the prickers are 

 carried. 



"Wires have been inserted in the wire-plates, both of 

 the transit circle and of the altazimuth, at intervals 

 adapted to the rapid observation by touch. The wires 

 of the transit circle, and the vertical wires of the altazi- 

 muth are adapted to intervals of about 42* and 48* of 

 arc ; the intervals of the horizontal wires of the altazi- 

 muth do not exceed 24" of arc. These are probably the 

 smallest intervals that have ever been used for similar 

 observations. The old systems of wires are not dis- 



