penetrating into Space by Telescopes. $g 



see borrowed illumination to the amazing distance of more than 

 18 hundred millions of miles ; especially when that light, in 

 coming from the sun to the planet, has to pass through an equal 

 space, before it can be reflected, whereby it must be so en- 

 feebled as to be above 368 times less intense on that planet 

 than it is with us, and when probably not more than one-third 

 part of that light can be thrown back from its disk.* 



The»range of natural vision with self-luminous objects, is 

 incomparably more extended, but less accurately to be ascer- 

 tained. From our brightest luminary, the sun, we pass imme- 

 diately to very distant objects ; for, Sirius, Arcturus, and the 

 rest of the stars of the first magnitude, are probably those that 

 come next ; and what their distance may be, it is well known, 

 can only be calculated imperfectly from the doctrine of paral- 

 laxes, which places the nearest of them at least 412530 times 

 farther from us than the sun. 



In order to take a second step forwards, we must enter into 

 some preliminary considerations, which cannot but be attended 

 with considerable uncertainty. The general supposition, that 

 stars, at least those which seem to be promiscuously scattered, 

 are probably one with another of a certain magnitude, being 

 admitted, it has already been shewn in a former Paper, -j- that 

 after a certain number of stars of the first magnitude have 

 been arranged about the sun, a farther distant set will come in 

 for the second place. The situation of these may be taken to 

 be, one with another," at about double the distance of the former 

 from us. 



* According to Mr. Bodguer, the surface of the moon absorbs about two-thirds 

 of the light it receives from the sun. See Trade d'Optique, page 122. 

 t Phil. Trans, for the year 1796, page 166, 167, 168. 



I 2 



