672 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



a high electrical conductivity. If the lengths of the two wires do not 

 together exceed fifty-five yards, then a wire of - 157 inches diameter 

 and of high conductivity will suffice. For longer distances it is 

 advisable to use a strand of larger diameter. 



The lamp used with the machine is regulated without clockwork, as 

 the employment of the latter has not only been a source of numerous 

 failures and difficulties, but is liable to disarrangement upon the 

 least rough usage. The lamp of itself regulates the carbon points, 

 keeping them at a uniform distance, and thus a perfectly steady light 

 is produced. 



