Magnetic Slate oj Iron and its Plioto- Electric Properties. 345 



Table I. 



Time in seconds taken for Leaf to move from to 10. 



A. 



B. 



C. 



Iron unmagnetized. 



Iron, North Pole. 



Iron, South Pole 



20-2 



17-2 



15-2 



14-8 



15-2 



156 



14-8 



15-8 



18'2 



17-0 



16/2 



164 



19-4 



17-2 



17-8 



156 



16-2 



16-4 



152 



14-8 



148 



15-2 



15-4 



160 



16-8 



16-4 



170 



186 



17-8 



21-2 



21-4 



19-8 



21-4 



196 



196 



21-2 



20-0 



19-2 



18-2 



18-4 



19-2 



18-8 



Mean. 



Mean. 



Mean. 



17-6 



17-1 



17-7 



Arc current = 2'3 amps. 

 Sensitivity of Electrometer, 10 scale divs. = 0*75 volt. 









Table II. 











Rise of Voltage per 



sec. 







A. 





B. 



C. 





riment. 



Unmagnetized 



North. 



South. 



Arc current 



1 



2 



3 



4 



5 



•061 

 •064 

 •046 

 •030 

 043 

 •046 

 •043 





•030 

 043 

 •047 

 •043 



•062 

 •066 

 045 

 •030 

 •044 

 •048 

 •044 



2'7 amps. 

 2'6 „ 



2-6 „ 

 26 „ 

 2-8 „ 



6 



7 



2-7 „ 

 2*3 „ 



Note. —The light was normal to the surface in all the above experiments. 



It would, perhaps, be advisable at this stage to consider 

 the possible effects of two disturbing factors on the results 

 obtained. These are (a) the direct effect of the magnetic 

 field on the path of the ions between the iron and the arid, 

 and (b) the possible effect of the roughness of the iron 

 surface. Let us first consider the effect of the magnetic 

 field. When the iron is unmagnetized, the photo-electron 



