REGISTRATION BY PHOTOGRAPHY 67 



the expected unequal impressions, two sensibly 

 identical images were obtained. I believe this 

 failure, unique, be it remarked, to be due to 

 an insufficient regulation of the spark, which, 

 doubtless, was not sensitive. Fig. 6 is a 

 photo -engraved reproduction of the prints 

 obtained with and without " N " rays issuing 

 from a Nernst lamp. 



Fig. 7, similarly, shows the result of an 

 experiment with " N " rays, produced by two 

 large files. 



Though the photogravures are far from 

 rendering in a satisfactory manner the aspect 

 of the originals, they nevertheless show the 

 influence of " N " rays on a photographic 

 impression. 



I give further (Figs. 8 and 9) the reproduc- 

 tion of photographs, showing that " N " rays, 

 issuing from a Crooke's tube, are polarized. 



These photographs date from the month 

 of April, 1903. They were not obtained by 

 the method of reiterated alternation of exposure, 

 as this method is difficult to apply to this 

 case ; but the experiments have been repeated 

 a great number of times with the most minute 



