249 



following work the air gap was 49 mm. and the current 22 amperes. In 

 order to obtain a photograph of the current which passed between the 

 points transverse to the magnetic lines of force it was necessary for the 



liglit fruui the pinlmle to jiass liii'ough Hk' linllow (-(ires of tlie magnet. 

 This was accouiiilislicd I)y lifting 11h' two portions of tlic lube against 

 the nuignet, as shown in jjliotograph, Fig. S. An auxiliary wooden tube 

 25 cm. square find 12.,") cnj. long wag placed between the coils of the 



