THE MOVEMENTS OF THE STARS. 279 



towards the red end. If the star retreated sufficiently fast, 

 its green colour would assume a yellowish hue ; were its 

 motion faster still, the yellow would be transformed into 

 a red, while if the speed be still further accelerated the red 

 would continually deepen corresponding to the lessened 

 number of waves that entered the eye in a second, until at 

 last the vibrations would become so slow that invisibility 

 would again result from the want of nerves on the retina 

 competent to perceive the vibrations of the character thus 

 presented. 



It was once supposed that the colours actually observed 

 in the stars might be, as a matter of fact, explained as 

 consequences of their varied movements to us and from us ; 

 the suggestion was an attractive one, but it will not bear 

 the light of examination. It must be particularly observed 

 that in the case we have supposed the light of the star is 

 strictly monochromatic, but this is a condition of things 

 which certainly does not exist in any ordinary star. In 

 fact, in this respect the radiation from the stars may be 

 said to resemble the radiations from the sun. There is an 

 immense variety of different coloured light blended to- 

 gether not only all the hues of the visible spectrum, but 

 abundance of ultra-violet rays and abundance of rays 

 beyond the red. If, therefore, as in our first case, the star 

 be so hurrying towards us that the green light from the 

 central parts of the spectrum is carried on towards the 

 blue, the place of the green is itself filled by other rays 

 advancing from the red end. The rays initially red have 

 their places taken by rays from the invisible ultra-red 

 region, which, by a quickening in the number of vibra- 

 tions perceived per second in consequence of the rapid 



