40 SPECIAL RESULTS IN THE URANOLOGICAL 



which should not present a fixed star (i. e. a sun), either the 

 entire vault of heaven, if light arrived to us quite un enfeebled, 

 must appear as luminous as our sun ; or, if this be not so, 

 that we must assume an enfeeblement of light in its passage 

 through space, or a decrease of the intensity of ]ight greater 

 than in the inverse ratio of the square of the distance. 

 Now, since we do not see such an almost uniform brightness 

 covering the heavens (to which Halley ( 79 ) also alludes in 

 reference to an hypothesis which he rejects), therefore, in 

 the view of Cheseaux, Olbers, and Struve, we must assume 

 that space is not absolutely and perfectly transparent. 

 Results which Sir William Herschel derived from his star 

 gaugings, ( 80 ) and from ingenious investigations on the 

 space-penetrating power of his great telescope, appear to 

 establish that, if the light of Sirius lost only ^^ on its way 

 to us in passing through a gaseous or ethereal fluid, this 

 loss, which would give the measure of the density of a light- 

 enfeebling fluid, would suffice to explain phenomena as they 

 present themselves. Amongst the grounds of doubt which 

 the illustrious author of the new " Outlines of Astronomy" 

 opposes to the supposition of Olbers and Struve, one of the 

 most important is, that in the greater part of the milky way, 

 in both hemispheres, his twenty-foot telescope shews him 

 the smallest stars projected on a black ground. ( 81 ) 



A better proof of the existence of a resisting fluid, ( 82 ) 

 and one, as I have already said, founded on direct observation, 

 is furnished by Encke's comet, and by the ingenious and 

 highly important conclusions to which it has conducted its 

 discoverer. The impeding medium must, however, be con- 

 ceived to be different from the all -penetrating ether whose 



