392 



Prof. Draper on the Production of Light by Heat 



the position subsequently to be occupied by the incandescent pla- 

 tinum. Fig. 1. represents the results of this observation. 



ABC D 



Eb 



F d 



G 



Ukl 



Fig. 1. 



6. 



|jjl>ayli g ht. 



2130 



5. 



I 

 1 



I 



fl 

 I 



* 



1440°. 



4. 



I 



t 



1325°. 



3. 



* 



1210°. 



2. 



A 



Hogs . 



Spectra of incandescent platinum at different temperatures. 



The strip of platinum was now placed in the position of the 

 fissure which had given the spectrum, fig. 1, and its temperature 

 was raised by the passage of a voltaic current. Although I could 

 distinctly see the metal when the heat had reached about 1000° 

 by the naked eye, yet the loss of light in passing the prism and 

 telescope was so great that I found it necessary to carry the tem- 

 lvrah "'" t0 1210° before a satisfactory nh^Prvnt inn ronld be made. 



peratur 



the 



~- «..o r i U me opecuuin extended trom the position ot me 

 line B in the red, almost as far as the line F in the green ; ~~ 

 colors present being red, orange, and a tint which may be desig- 

 nated as gray. There was nothing answering to a yellow. The 

 first rays visible through this apparatus may therefore be desig 



nnfP/1 »c rar) on/-l ,-».. — „ :_ t. - .i <* • «t till 



nated 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. 



u u_._ current was now j ncrease( j j an( j t he temperature 



The red end of the spectrum remained nearly 



rose to 1325°. 



tion 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 considerably be- 

 yond the line G, as shown in fig. 5. 



Oil bringing the platinum to 2130° all the colors were present, 

 and exhibited considerable brilliancy. Their extent "was some- 

 what shorter than that of the daylight spectrmn, as is seen in 



