4 



ON THE AUKORAL SPECTRUM 



I American Journal of Science [3], F, 320, 1873] 



A letter from Henry A. Rowland, at present Instructor in Physics in 

 the Rensselaer Polytechnic Institute at Troy, informs us that he 

 observed the line of wave-length 431 in the auroral spectrum of last 

 October. He says : " The observations were made with an ordinary 

 chemical spectroscope of one prism, in which the scale was read by 

 means of a lamp. Great care was taken in the readings, and after com- 

 pleting them the spectroscope was set aside until morning, when the 

 readings were taken on the lines of comparison without altering the 

 instrument in any way or even regulating the slit. The wave-lengths 

 of the known lines were taken from Watts's * Index of Spectra/ but as 

 he does not give the wave-lengths of lines in the flame spectrum I am 

 not quite certain that they are correct." On the scale of his instru- 

 ment, Li a was at 13.5, Ca a 21, Naa27.5 , Ca/336 , Ca r 95.5, and 

 K/s 110. The aurora lines were as follows: 



Scale-reading. Wave-lengths. 



1 19 628.3 



2 35.5 554.3 



3 95 425 



" The wave-lengths of the auroral lines were obtained by graphical 

 interpolation on such a large scale as to introduce little or no error." 



