259 



wooden l)l(ick by two binding' posts in order to nialce connection witli the 

 battery. The photographic plate was so mounted back of a block of 

 wood al)out '2~^ cm. long-, 14 cm. wide and 4 cm. thick with a hole 2M> 

 em. in diameter that it could be slid past the opening and a number of 

 exposures made upon one plate. 



MB R/AP. 

 3.0SEC. 



PL/ITE, I, 



The tirst two photographs taken wivh the apparatus just described 

 with the time of exposure and current as indicated. There is very little 

 if any difference between those marked X and the others. Those marked 

 N are exposures without a lead screen inserted between the source and 

 the platinum wire. 



