9 8 



INFRA-RED REFLECTION SPECTRA. 



The aluminum was a sheet of commercial material. It took a high 

 polish. Its reflecting power is unusually high beyond lo/x, and is 

 known to be practically a perfect reflector for heat waves at 25 //,. 



Little can be said concerning tin. It was found impossible to give it 

 a polish, although the melted surface on cooling was very bright. From 

 its electrical conductivity it ought to have a reflecting power of the 

 order of nickel and platinum. 



\^^^ 



-JO-fc^ 



678 



FIG. 82.- -Pure metals. 



Zinc is the most interesting of all the metals studied. It takes an 

 unusually high polish which is quite permanent. Its color is peculiar. 

 It seems to have a low reflecting power in the visible spectrum, which 

 rises suddenly to a maximum beyond 4 p, and in this respect compares 

 favorably with silver, which is the highest and most serviceable reflector 

 known for the visible and the infra-red spectrum. The electrical con- 

 ductivity, as well as the reflecting power, of zinc and of cadmium are 

 close in agreement. 



The indium mirror was obtained by polishing a sheet about 3 by 

 2 by o.i cm. It was not free from scratches, but took a high polish. It 

 has a slightly higher reflecting power than platinum. Its electrical con- 



