Curiosities of Science. 85 



was produced in the focus of Parker's burning lens, 32 inches 

 in diameter, which inelts crystals of quartz and agate.* 



THE MILKY WAY UNFATHOMABLE. 



M. Struve of Pulkowa has compared Sir William Herschel's 

 opinion on this subject, as maintained in 1785, with that to 

 which he was subsequently led ; and arrives at the conclusion 

 that, according to Sir W. Herschel himself, the visible extent 

 of the Milky Way increases with the penetrating power of the 

 telescopes employed ; that it is impossible to discover by his 

 instruments the termination of the Milky Way (as an inde- 

 pendent cluster of stars) ; and that even his gigantic telescope 

 of forty feet focal length does not enable him to extend our 

 knowledge of the Milky Way, which is incapable of being 

 sounded. Sir William Herschel's Theory of the Milky Way was 

 as follows : He considered our solar system, and all the stars 

 which we can see with the eye, as placed within, and consti- 

 tuting a part of, the nebula of the Milky Way, a congeries of 

 many millions of stars, so that the projection of these stars 

 must form a luminous track on the concavity of the sky ; and 

 by estimating or counting the number of stars in different di- 

 rections, he was able to form a rude judgment of the probable 

 form of the nebula, and of the probable position of the solar 

 system within it. 



This remarkable belt has maintained from the earliest ages 

 the same relative situation among the stars ; and, when exa- 

 mined through powerful telescopes, is found (wonderful to 

 relate !) to consist entirely of stars scattered by millions, like 

 glittering dust, on the black ground of the general heavens. 



DISTANCES OF NEBULA. 



These are truly astounding. Sir William Herschel esti- 

 mated the distance of the annular nebula between Beta and 

 Gamma Lyrse to be from our system 950 times that of Sirius ; 

 and a globular cluster about 5g south-east of Beta Sir William 

 computed to be one thousand three hundred billions of miles 

 from our system. Again, in Scutum Sobieski is one nebula in 

 the shape of a horseshoe ; but which, when viewed with high 

 magnifying power, presents a different appearance. Sir William 

 Herschel estimated this nebula to be 900 times farther from us 

 than Sirius. In some parts of its vicinity he observed 588 

 stars in his telescope at one time ; and he counted 258,000 in 

 a space 10 long and 2 wide. There is a globular cluster 

 between the mouths of Pegasus and Equuleus, which Sir Wil- 



* For several interesting details of Comets, see " Destruction of the World 

 by a Comet," in Popular Errors Explained and Illustrated, new edit. pp. 165-168. 



