472 



REPORT — 1894. 



In describing this new step which is to give us a linear spectrum, in 

 addition to the original curve, it will be desirable to also give evidence of 

 the statement now made, that the present method is capable of recording 

 far minuter inflections than those shown in the curves exhibited (Plate II), 

 which, as has just been stated, have been taken only for the purpose of 

 illustrating such more important features as can be seen and verified by 

 the audience, and especially for showing the agreement of indeperdent 

 observations. The evidence of the capacity of the apparatus to show this 

 detail will best be illustrated by applying our purely thermometric method 



Fig. 2. 



to some well-kjiown lines in the visible spectrum, such as the familiar 

 ' D ' lines of sodium. I have already stated that ten years ago the bolo- 

 meter was barely able to distinguish this as a single line. At the present 

 time our little thermometer, as you see (fig. 2), now shows not only the two 

 ' D's ' as separate lines, but the nickel line between them. First we have 

 the complex energy curve, where we see successively the inflections due 

 to the motions of the galvanometer caused by the cold in D,, then to the 

 smaller chill from the nickel line (aided, perhaps, Ijy that from some of 

 the close atmospheric lines), then the chill from D2. 



