1U 



Mr. J. A. Fleming on the Polarization of 



the slit was reflected on to a scale in the usual way, and the 

 image viewed through a telescope placed behind the galvano- 



fm^WrW^l 



W. Wheatstone's bridge. 



D. Daniell's cell. 



T. Tangent-galvanometer. 



V. Voltameter. 



G. Mirror-gal vanoscope. 



K. Key. 



S. Tube to Sprengel pump. 



meter. By this means it was found possible to detect and 

 read deflections of the needle amounting only to ^ of a degree 

 with great ease. With this delicate arrangement it was a 

 matter of great difficulty to get the platinum plates perfectly 

 neutral. The last traces of polarization from previous experi- 

 ments subsided with extreme slowness. The following opera- 

 tions were then performed : — 



(i) The electrodes were made perfectly neutral. 



(ii) The galvanometer excluded from the circuit, and a direct 

 current sent through the decomposing-cell for one minute. 



(iii) The polarization measured by the swing made by the 

 galvanometer-needle when the electrodes were suddenly con- 

 nected with it. 



(iv) The swing or excursion made by the needle when the 



