

150 M. Colladon on the Deviation of the Magnetic Needle. 



galvanometer began to deviate. At a distance of one or two 

 centimetres, the deviation became 23°. It then grew weak- 

 er, and vanished after a duration of five seconds. The direc- 

 tion of the deviation was in the direction of the current, and 

 the direction was changed by presenting to the battery the 

 same extremity of the galvanometer. Opposite directions were 

 also obtained, by charging the battery alternately with posi- 

 tive and negative electricity. 



In dry weather, M. Colladon obtained deviations of three 

 or four degrees, by using the simple electrical machine, and 

 also Nairne's machine for two electricities, or a plate machine 

 of five feet. 



M. Colladon next soldered to the extremities of his galvano- 

 meter a platina wire, and when one of the soldered pieces was 

 kept at the temperature of 32°, while the other was heated 

 in a mercurial bath to the temperature of 313° Fahr. a devia- 

 tion of 45° took place. Hence it follows, that the electricity 

 which may be accumulated in a given time in a battery, or 

 even in a conductor, is a finite portion of that which circulates 

 during the same time in a closed electromotive circle. 



M. Colladon then proposes to use the galvanometer in place 

 of an electrometer, for measuring small quantities of electricity 

 accumulated in batteries, or drawn off by points. With this 

 view he prepared a galvanometer with 500 turns, having its 

 wire not only doubly covered with silk, but each series of turns 

 covered with gummed taffetas. With the plate glass machine 

 with which he obtained a deviation of 3° or 4°, he now ob- 

 tained 



At 1 decimetre of distance a deviation of - 18° 



2 - - 10 



4 - 5\ 

 8 - - 8 

 1 metre, - - - 2 



5 centimetres, - - 19 

 24 cent. - 20 

 1 cent. - 20 



A single Leyden phial, with two square feet of surface 

 made the needle deviate 32° when it was fully charged. 



In another section of his paper, M. Colladon treats of at- 

 mospheric electricity, and he shows that the galvanometer is 



