REPORT OF THE SECRETARY. 



61 



Complete records of all of these bologriiphic curves have been kept iu the hook 

 specially jirovided for that purpose, and from them hy auother automatic process are 

 produced the linear spectra of which an illustration follows. As elsewhere stated, 

 the result of the year's work has been the discovery and approximate determination 

 of position of about 150 or 200 new lines in this hitherto almost unexjjlored region. 



The accompanying illustration of one of the "rock-salt" spectra of the invisible 

 spectrum obtained by the new process is intended to give a general, if crude, idea of 

 the novelty, the extent, and (it may be hoped) the value, of this field of labor. 



The visible solar spectrum, first investigated by Sir Isaac Kewton, is represented 

 as to its length by the blank space on the left; the number .4 (i. e., the part where 

 "wave-length is four-tenthd of a micron) and .8 {i. e., the part where wave-length is 

 eighth-tenths of a micron) representing the extremities of the solar spectrum as 

 known to him. 



Below this all is invisible, and the investigations made at this Observatory by the 

 novel bolometric methods here referred to have been chiefly instrumental in carrying 

 the mapping of lines to 6.0 (six microns), or through nearly thirteen times the extent 

 known to Newton. Tlie great majority of all the lines which till this space have 

 been discovered and laid down by the new bolometric method, and most of them 

 here in Washington during the last two years. 



B. The special holographic work, which is carried on during the cloudy weather, 

 during which the regular work is necessarily interrupted, includes the classification, 

 detailed examination, and, finally, the reduction of the holographs taken to linear 

 representatives of the infra-red spectrum, in which the final result is a line photo- 

 graph which is precisely similar, as far as automatic reduction processes will admit, 

 to the line spectrum photographs of the visible part of the sjiectrum. Owing to the 

 labor involved in this reduction it has been deemed desirable to apply this process 

 of reduction only to the best of the holographs taken. The result of this portion of 

 the work is briefly summed up as follows: 



Line spectrum photographs. . 



Bolosraphs 



reduced for the 



month of — 



1892. 



July 



August 



September.., 



October , 



November . . . 



December . . 

 1893. 



January . . 

 February . 



March . 

 April . . 



May . 



June. 



Number. 



Character of holograph. 



Taken with glass prism 



Taken with rock salt prism 



-do 

 .do 



Kegion represented . 



Taken with glass prism Infra-red spectrum down to wave 



length A = 2-5 M. 

 Do. 



Infra-red spectrum down to wave 

 length A = 2-5/». 

 Do. 

 Infra-red spectrum down to wave 

 length A = 5^i.. 

 Do. 

 Do. 



Total from glass prism 28 



Total from rock salt prism 11 



Aggregate. 



These represent complete line spectrum charts of the invisible portion of the 

 spectrum down to about 2-5// for the glass and 5// for the rock salt prism. 



