538 Prof. Trowbridge and Mr. Crandall on Groove-Form 



central image. The mean angle about which the energy is 

 disposed is 20°-25° from the position of the central image. 

 As the wave-length is increased, the orders move farther 

 and farther out from the central image, consequently the 

 energy becomes concentrated in lower orders during the 

 process. Beginning with wave-length 2*8 yu, the first order 



Fig-. 2 



fercent of Total Energy 

 in first Order Sped torn 



Brackett G rating No W 



predominates, and since there cannot be fractional orders 

 of spectra, it is evident that more and more of the energy 

 will be thrown into this order as the wave-length is increased, 

 a conclusion which is wholly substantiated by the curves for 

 greater wave-length, A curve is plotted (fig. 2) showing 



