On the Transparency of the Ether. 15 



In the case of the heavenly bodies there should then be a 

 coloration, becoming more marked with the distance, this col- 

 oration also depending in part on the intensity. No regular 

 gradation in hue is perceptible, and hence it may be concluded 

 that the loss of energy is small, if any. From what is known 

 of the spectra of incandescent bodies, the effect of increase of 

 temperature is to displace slightly the position of maximum 

 energy up the spectrum. Any irregular distribution of stars 

 as regards temperature would not cause the average light of 

 a certain number in one part of the heavens to differ materi- 

 ally from that of another number taken anywhere else in the 

 heavens. To carry the test for absorption to the utmost 

 limit possible, we have only to consider those milky patches 

 of light visible to the eye in the Galaxy ; or, better, those star 

 clusters which are barely resolvable with the best telescopes ; 

 or, going still further, to consider those nebulae whose spectra 

 resemble the stellar spectra, and which consequently are 

 probably resolvable into stars. From the vast number of 

 stars which must constitute such a stellar mass, it may be 

 concluded that if there were no absorption, the light with 

 which such a mass would shine would be white. In travers- 

 ing such vast distances, the absorption must be infinitesimal, 

 not to produce a perceptible coloration. The general absence 

 of gradation in color, even in the remotest visible bodies, 

 shows that but a small per cent of their light can have been 

 lost in space. This shows that er'^'^y cannot differ from unity 

 by more than a small quantity. Hence Ky will in general be 



less than unity, and k will not be greater than -, which for the 



distances we have been considering, is excessively small. 

 Referring to equation (10), we see that iv is nearly unity, and 

 hence the difference in time of propagation is a very small 

 quantity, even for the remotest visible bodies. 



Taking now our complete equation as it would be for plane 

 polarized light propagated in spherical waves, we have for the 

 intensity at any point 



y- ■ 

 15 



