"HITTER'S DARK RAYS" 159 



prove. He could and did show that a thermometer 

 rose in passing from the violet to the red end of the 

 spectrum : but he did more. He placed the ther- 

 mometer beyond the visible red, and found that, as it 

 continued to rise, heat-rays, invisible to the eye and 

 less bent from the straight path of the sunbeam, gave 

 the greatest heat. He must have asked himself, Is 

 there not something similar at the violet end ; but he 

 had not the means of answering the question. He did 

 what was next best. He asked a question pregnant 

 with great results, and destined to bear an abundant 

 harvest for the welfare and instruction of man. " It 

 may be pardonable if I digress for a moment, and 

 remark, that the foregoing researches ought to lead us 

 on to others. May not the chemical properties of the 

 prismatic colours be as different as those which relate 

 to light and heat : . . . they may reside only in one of 

 the colours." To this question he could neither give 

 nor get an answer. A short time passed, and the 

 answer came from Germany and, independently, from 

 England. " The existence of solar rays accompanying 

 light, more refrangible than the violet rays, and 

 cognisable by their chemical effects, was first 

 ascertained by Mr. Ritter." They were called "The 

 dark rays of Ritter," and " appeared to extend beyond 

 the violet rays of the prismatic spectrum, through a 

 space nearly equal to that which is occupied by the 

 violet." "Paper dipped in a solution of nitrate of 

 silver" was used to prove the existence of these 

 chemical rays and to introduce the days of photo- 

 graphy. It was most fitting that it should be so. 

 An astronomer led the way in this new quest after 

 invisible rays ; chemistry supplemented his discoveries 



