METALS. 



97 



here that the change in reflecting power with angle of incidence is the 

 same for all the metals examined, and, since we are rinding a ratio, will, 

 therefore, affect alike the numerator and denominator of the fraction. 

 Any error thus introduced could be only a fraction of a per cent, which 

 is as accurate as the variation in the polish of different samples of the 

 same metal will permit. The low reflecting power of most of the 

 metals examined in the region of I p, is due more to lack of polish and 

 planeness of surface than to a possible transparent region such as 

 obtains in silver, in the ultra-violet. Palladium is lower in reflecting 

 power than platinum; and it is barely possible that it would have a 

 slightly higher value if a better surface could be produced. The speci- 

 men was made by soldering a o.i mm. sheet upon a heavy plate of brass. 



TABLE I. REFLECTING POWER OF METALS. 



[Absolute values.] 



Considerable difficulty was experienced in casting a homogeneous 

 plate of cadmium. Success was finally attained by melting it in a thin 

 copper mold. When cool the mold was torn off and the ( i cm. thick) 

 plate filed and ground plane. In fig. 82 it will be noticed that its 

 reflecting power suddenly rises to a constant value beyond 5 /*,. 



The sheet of cobalt was about 0.5 mm. thick, and permitted consider- 

 able filing and grinding. However, it was found impossible to prepare 

 a surface that was free from pores. This probably explains its devia- 

 tion in reflecting power from that of nickel, out to 10 p, where it reflects 

 more than nickel, as it should, since its electrical conductivity is higher. 











rs v 



