THE NEW SPECTRUM. (',91 



is more than the number of visible ones in Kirehoff & Bunsen's chjiits. 

 The position of each line is fixed from a mean of at least six indepen- 

 dent determinations with the accuracy stated above. 



The reader will perhaps gather a clearer idea of this action if he 

 imagines the map before him hung up at right angles to its actual posi- 

 tion, so that a rise in the energy curve given would be seen to corre- 

 spond to a deflection to the right, and a fall, to one to the left: for in 

 this way the deflections were written down on the jnoving photo- 

 graphic plate from which this print has been made. The writer was 

 now speaking of the refinements of the most recent practice: l>ut tiiere 

 was something in this retrospect of the instrument's early use which 

 brought up a personal reminiscence which he asked the Academy to 

 indulge him in alluding to. 



This was that of one day in 1881, nearly twenty years ago, when 

 being near the summit of Mount Whitney, in the Sierra Nevadas. at 

 an altitude of 12,000 feet, he there, with this newh' invented instru- 

 ment, was working in this invisible spectrum. His previous experi- 

 ence had been that of most scientific men — that very few discoveries 

 come with a surprise, and that the}^ are usually the summation of the 

 patient work of 3"ears. 



In this case, almost the only one in his experience, he had the sensa- 

 tions of one who makes a discovery. He went down the spectrum, 

 noting the evidence of invisible heat die out on the scale of the instru- 

 ment until he came to the apparent end even of the invisibk\ beyond 

 which the most prolonged researches of investigators up to that time 

 had shown nothing. There he watched the indications grow 

 fainter and fainter until they too ceased at the point where the 

 French investigators believed they had found the very end of the end. 

 By some happy thought he pushed the indications of this delicate 

 instrument into the region still beyond. In the still air of this lofty 

 region the sunbeams passed unimpeded by the mists of the lower 

 earth, and the curve of heat, which had fallen to nothing, began to 

 rise again. There was something there. For he found, suddeidy and 

 unexpectedly, a new spectrum of great extent, wholly unknown to 

 science and whose presence was revealed by the new instrument, the 



bolometer. 



This new spectrum is given on the map, where it will bi' observed 

 that while the work of the photograph (much more detailed than that 

 of the bolometer, where it can be used at all) has been stated to 

 extend, as far as regular mapping is concerned, to about l.K that 

 everything beyond this is due to the bolometer, except that early 

 French investigators had found evidence of heat extending to I cV. 

 Still beyond that ultima thule, this region, which he has ventured to 

 call the "New Spectrum," extends. It will be found between wave- 

 lengths 1.8'^ and 5.3'" on the map. 



