Chap. X.] 



WlEDEMA NN 's Bo US SOLE. 



connected above with a light frame which holds a 

 circular plane mirror B. To prevent currents of air 

 from moving the mirror, a circular brass cover c 

 encloses it. The cover has a circular window w in 

 front, through which the mirror can be viewed. Above 

 the mirror is screwed a long glass tube, which carries 



Fig. 56. Wiedemanu's Galvanometer (Boussole). 



at the top, on a little ebonite support, a little windlass, 

 whose centering on the glass tube is regulated by three 

 little screws. On it is wound a single filament of silk, 

 which passes down the glass tube through an opening 

 in the ebonite. At the end of the silk fibre is a loop, 

 to which a small platinum hook is attached, which 

 suspends the mirror and magnet by an eye in the 

 mirror frame. By this arrangement the needle can be 

 raised or lowered, and centered in the copper chamber. 

 The copper chamber and its attachments are supported 



