76 



Intelligence and Miscellaneous Articles. 



Fig. 1. Fig. 2. 



Calc Spar. 



Normal. 



Abnormal. 



Since the rays which produce these abnormal figures do not act 

 upon iodide of silver, but affect bromide whether a quinine bath 

 be interposed or not, they can hardly be present in the more refran- 

 gible, invisible portion of the spectrum, or at least not in that part 

 which is absorbed by sulphate of quinine ; neither can they be in- 

 visible heat rays beyond the extreme red, since these do not affect 

 bromide of silver. I have satisfied myself that the figures are in- 

 visible to the eve, by accurately examining each of the crystals in 

 a polariscope, illuminated first by white light, and then by each iso- 

 lated ray of a very pure solar spectrum ; in no case was there any 

 figure but the normal one perceived. It is possible, therefore, that 

 these abnormal figures may be caused by invisible rays which have 

 hitherto escaped notice, existing within the space enclosed by the 

 visible spectrum. 



