Focal Isolation of Long Heat- Waves. 



255 



elementary vertical strips, each one of which represents nearly 

 homogeneous radiation. We now draw the interference 

 curves (sine curves) of the various strips, and the super- 

 position of all these curves should give us a curve identical 

 with the curve obtained with the interferometer, if our 



energy curv 



e Ires been correctly figured. 



Curves a and b (fig. 4) examined in this way 



gave curves 



Fig. 4. 



ffO 



90 



7£< 





a 









































































l 











J 



f"**\ 











l\ 













J) 













i! 













120 1W 160 180 209 



resembling very closely the interference curves of figs. 2 

 and 3, and may be considered as representing the approximate 

 distribution of energy in our radiation. It is thus apparent 

 that we have experimental evidence of the presence of heat- 

 waves certainly 150 yu, and probably 200 fi in length. 



Absorption and Reflexion of the Isolated Radiation. 



Notwithstanding the wide spectral range of our isolated 

 radiation, it seemed of interest to determine the reflecting 

 and absorbing power of a variety of substances for these 

 rays, which belong to a region of the spectrum about which 

 we know nothing, and have, up to the present time, been 

 unable to investigate with homogeneous rays. We com- 

 menced with the investigation of transparent solids, placing 



