896 Profs. Trowbridge and "Wood on Groove- Form and 



from the circumstance that the 29° edge was double. The 

 intensity distribution was as follows : — 



Quartz Ears. C0 2 Rays. 

 Central image 17 Central image 168 



First order, left ..,57 2nd order, left ...37 



3rd „ ,, ... 39 

 1st „ right... 7-2 



right... 26 3rd „ „ ... 39 



*e>- 



The oblique image lies at 29° to the left, midway between 

 the 2nd and 3rd order spectra of the C0 2 rays, consequently 

 they contain very nearly the same amount of energy. The 

 first order to the left is absent, but it is present on the right- 

 hand side, though feeble. 



The quartz rays show a remarkable concentration in the 

 first order spectrum which contains 57 per cent, of the total 

 energy. With the C0 2 rays we again find concentration 

 owing to shorter wave-lengths, for the two spectra, which lie 

 symmetrically to the right and left of the oblique image, 

 contain together 76 per cent, of the energy. 



Grating No. 7. Constant, "0123 mm. 



Angle of Planes, 30° and 20°. 



The 20° planes were rough, reflected poorly, and gave no 

 oblique image. The 30° planes were excellent, and there 

 was no visible central image. The intensity distribution was 

 as follows : — 



Quartz Rays. 





C0 2 Rays. 





Central image . . . 



52 



1st order, left .. 



2 



First order 



48 



„ right.. 



6 







2nd „ left .. 



63 







3rd „ „ .. 



6 







Central image . . 



23 



Here again we have the first order spectra practically 

 absent for the C0 2 rays, while the second order contains 

 63 per cent, of the total energy, the largest thus far obtained. 

 The third spectrum in this case is very weak. 



With grating No. 6 the 2nd and 3rd order spectra were 

 of equal intensity, yet there is very little difference between 

 the gratings when examined optically, except the very inferior 

 reflecting power of the 20° planes in the case of No. 7. 

 Owing to the powerful concentration of the energy in the 

 2nd order spectrum, fainter outlying parts of the C0 2 band 

 appear reaching nearly to the 3rd order spectrum of the 

 strong portion. 



