THE STELLAR UNIVERSE. 379 



These phenomena led Sir William Herschel to the conclusion that the stars 

 of our firmament, instead of being scattered in all directions indifferently 

 through space, form a stratum, of which the thickness is small in comparison 

 with its length and breadth ; and in which the earth occupies a place some- 

 where about the middle of its thickness, and near the point where it subdivides 

 into two principal laminae, inclined at a small angle to each other. For it is 



Fig.i. 



certain that, to an eye so situated, the apparent density of the stars, supposing 

 them pretty equally scattered through the space they occupy, would be least 

 in a direction of the visual ray (as S A), perpendicular to the laminae, and 

 greatest in that of its breadth, as S B, S C, S D ; increasing rapidly in pass- 

 ing from one to the other direction, just as we see a slight haze in the atmo- 

 sphere thicking into a decided fog-bank near the horizon, by the rapid increase 

 of the mere length of the visual ray. Accordingly, such is the view of the 

 construction of the starry firmament taken by Sir William Herschel, whose 

 powerful telescopes have effected a complete analysis of this wonderful zone, 

 and demonstrated the fact of its entirely consisting of stars. So crowded are 

 they in some parts of it, that by counting the stars in a single field of his tele- 

 scope, he was led to conclude that 50,000 had passed under his review in a 

 zone two degrees in breadth, during a single hour's observation. The im- 

 mense distances at which the remoter regions must be situated, will sufficiently 

 account for the vast predominance of small magnitudes which are observed 

 in it.* 



The appearance which this mass of stars would present if viewed from a 

 position directly above its general plane, and at a sufficient distance to allow 

 its entire outline to be discerned, was represented by Sir William Herschel as 

 resembling the annexed drawing, fig. 2. 



He considered that it was probable that the thickness of this led of stars was 

 equal to about eighty times the distance of the nearest of the fixed stars from 

 our system ; arid supposing our sun to be at the middle of this thickness, it 

 would follow that the stars on its surface in a direction perpendicular to its 

 general plane would be at the fortieth order of distance from us. The stars 

 placed in the more remote edges of its length and breadth he estimated to be 

 in some places at the nine-hundredth order of distance from us, so that its ex- 

 treme length may be said to be in round numbers about two thousand times 

 the distance of the nearest fixed stars from our system. Such a space light 

 would take twenty thousand years to move over, moving all that time at the 

 rate of two hundred thousand miles between every two ticks of a common 

 clock ! 



The great splendor of that part of the Milky Way which passes through 

 the southern hemisphere, and some other peculiarities which he has remarked 

 in it, has suggested to Sir John Herschel a corroboration of his father's theory 

 of its form. " The general aspect of the southern circumpolar region," says 5 

 Sir John, " including in that expression 60 or 70 of S. P. D.,f is in a high 

 degree rich and magnificent, owing to the superior brilliancy and larger de- 

 velopment of the Milky Way : which, from the constellation of Orion to that 

 of Antinous, is in a blaze of light, strangely interrupted, however, with vacant 

 * Herschel 's Astronomy, chap. x. t Southern polar distance. 



