WOOD. NITROSO-DIMETHYL-ANILINE. 57 



possible to form a rough estimate of the reflecting power in different 

 parts of the spectrum. A similar series was made with a flat reflector 

 of magnalium, which is remarkably constant in reflecting power through- 

 out the entire spectrum. It was found that the nitroso, in the region of 

 its absorption band, reflected almost as strongly as magnalium, while just 

 on the ultra-violet side of the band there was a gap in the spectrum, due 

 to the very low reflecting power which the substance has for these waves. 

 The reflection coefficient at this point was estimated at about 2 per cent 

 only, while a short distance further up the spectrum the coefficient is at 

 least 80 per cent.* This indicates that the refractive index has a very 

 low value at the point of minimum reflection. The following table gives 

 an idea of the reflecting power of the nitroso in the various regions of 

 the spectrum as compared with the magnalium. The values are of course 

 only approximate, being deduced by picking out two spectra (one from 

 nitroso the other from magnalium) which showed the same intensity at 

 the given wave-length and then comparing the times of exposure. The 

 reflecting power is expressed as a fractional part of the reflecting power 

 of magnalium. 



"When the incidence angle is increased and the reflected light ex- 

 amined with a Nicol prism, a most beautiful surface color appeared, 

 ranging from a brilliant blue, through violet, to a reddish purple. This 

 is very easy to understand. The violet light within the region occupied 

 by the absorption band is metallically reflected at all angles of incidence, 

 consequently it is always present in excess in the reflected light, and is 

 never cut off by the Nicol. As the angle of incidence is increased, the 

 polarizing angle for red light is first reached, and the red end of the 

 spectrum disappears, being cut off by the Nicol, the reflected light 

 appearing blue. As the angle increases, more of the spectrum is re- 

 moved by the Nicol, and the color changes to deep violet, the dark 



* This value is much too high. It was based on the supposition that the magna- 

 Hum plate reflected 80 per cent, which was subsequently found to be incorrect, the 

 metal containing too little magnesium and having a rather low reflecting power. 



