Prof. Draper on the inoduclion of Light hy Heat. 349 



from the position of the fixed line B in the red, almost as far 

 as the line F in the green ; the colours present being red, 



Spectra of incandescent platinum at different temperatures. 



orange, and a tint which may be designated as gray. There 

 was nothing answering to a yellow. The first rays visible 

 through this apparatus may therefore be designated as red and 

 greenish gray ; the former commencing at the line B, and the 

 latter continuing to F. The magnitude and other relations 

 of this spectrum are given in fig. 3. 



The voltaic current was now increased, and the tempera- 

 ture rose to 1325''. The red end of the spectrum remained 

 nearly as before, but the more refrangible extremity reached 

 to the position of the little fixed line d. Traces of the yellow 

 were now visible; and, with a certain degree of distinctness, 

 I could see red, orange, yellow, green, and a fringe of blue. 

 Fig. 4 shows the result. 



The temperature was now carried to 1440°. I thought the 

 red extremity was advancing more to the line A : the blue 

 had undergone a well-marked increase. It reached consider- 

 ably beyond the line G, as shown in fig. 5. 



On bringing the platinum to 2130° all the colours were 

 present, and exhibited considerable brilliancy. Their extent 

 was somewhat shorter than that of the daylight spectrum, as 

 is seen in fig. 6. 



Having thus by repeated experiments ascertained the con- 

 tinued extension of the more refrangible end as the tempera- 

 ture rose, it became necessary to obtain observations for points 

 below 1210^ the limit of visibility through the telescope. I 

 therefore carried the prism nearer to the platinum, and look- 

 ing with the unassisted eye directly through it at the refracted 

 image, I ibund il could be distinctly seen at a temperature as 



