NUMBER OF STARS.] 



ASTRONOMY. 



951 



order, a, ft, y, S, t, cfcc., they now appeared according to 

 the order n, 7, t, ft, and i ; in Aquila they had changed 

 to the order a, 7, S, ft, t ; in Draco, to <y, ft, S, a ; in, 

 Leo, to a, 7, ft, f, t ; and this change was apparent in 

 numerous other instances. But it would now appear as 

 if the magnitudes of the stars had been carelessly in- 

 serted by Bayer, no such change being due to the objects 

 themselves. 



NUMBER OF STARS. In our estimation of the num- 

 ber of the fixed stars, it would appear that we are liable 

 to an illusion ; and that the generality of individuals 

 suppose a much greater number to be visible than is 

 found to be the case. The attention is probably directed 

 to the richest portions of the heavens ; and it may not 

 unfrequently happen that the judgment is biased by 

 what we have heard or read, rather than by what we see. 

 In this case, it may naturally be supposed that other 

 parts of the surface of the heavens are equally crowded 

 with stars, though they are not so bright or apparent as 

 the part which we really have in view ; and it may thus 

 be erroneously concluded that thousands of stars are 

 visible at the same moment, which only exist in imagi- 

 uation. When we come to test this conclusion by abso- 

 lute proof, it is found to be vastly out of proportion to 

 these impressions. The whole number of stars visible to 

 the naked eye in the central parts of Europe viz., those 

 included in the whole surface of the heavens north of 

 the equator, and including a zone of 30 of south de- 

 clination, comprising nearly eight-tenths of the whole 

 sky only amounts to 3,256 ; so that scarcely more than 

 2,000 stars can be visible to the naked eye, and above 

 the horizon, at the same moment. 



An attempt has been made to ascertain the number of 

 stare of different magnitudes by supposing them to be 

 situated at equal distances from one another, and that 

 they are all of the same absolute magnitude, but ap- 

 pearing differently in consequence of their various dis- 

 tances. There being fourteen stars of the first magni- 

 tude, we are to suppose them arranged at equal distances 

 upon a sphere : supposing the stars of the second magni- 

 tude to be twice the distance of those of the first, the 

 surface over which they would be scattered would be four 

 times that of the former ; and if placed at the same dis- 

 tances from each other, it would take fifty-six stars to 

 cover this area. The sphere of stars of the third magni- 

 tude would be nine times the area of that of the first, 

 and it would consequently take one hundred and twenty- 

 six stars to fill that surface ; and in a similar manner there 

 would be two hundred and twenty-four on the fourth, 

 three hundred and fifty on the fifth, and so on. This law, 

 however, does not correspond with the observed number 

 of stars of different magnitudes, there being seventy 

 stars of the second, and three hundred of the third a 

 much greater number than would exist on this supposi- 

 tion. Various other hypotheses have been formed to 

 show the probable number of stars, of different magni- 

 tudes, visible on a given portion of the sky ; but the 

 data are too inconclusive and vague to secure any degree 

 of accuracy in the result. 



It would be difficult to determine the number of stirs 

 fainter than those of the sixth magnitude. The catalogue 

 of Lalande (called the Histoire Celeste, and published at 

 the latter part of the last century) contains the places of 

 about 50,000 stars visible from the north pole to 25 of 

 south declination, and including those from the first to 

 tin- ninth magnitude. The zone included between 15 of 

 north, and 15 of south declination, contains, according 

 to the more modern observations of the illustrious Bessel, 

 31,085 stars, viz. : 



CC4 bright stars from the 1st to the Cth magni- 

 tude. 



2,500 of the 7th magnitude. 

 8,183 8th 

 10,738 9th 



Stars fainter than those of the ninth magnitude increase 

 in number in a wonderful degree ; and Struve concludes 

 that the number of stars visible in the twenty-feet tele- 

 tcope of Herschel, in the same zone of 30 in breadth 

 observed by Bessel, amounts to the enormous number of 



5,819,000, by far the greater number of which are situated 

 at those parts where the Milky Way intersects the equator 

 at six and eighteen hours of right ascension. Nor will 

 this appear overrated, when we recollect that on one 

 occasion Herschel perceived that nearly 120,000 stars 

 passed through the field of view of his telescope (15' in 

 diameter) in a quarter of an hour. The stars observed 

 by Herschel appear to have been situated in the following 

 order in respect to their right ascension ; and their density 

 as they approach the Milky Way becomes immediately 

 apparent. 



From Ih. to 5h. of right ascension 301,700 stars. 



5h. 



9h. 

 13h. 

 17h. 

 21h. 



9h. 

 , 13h. 

 ,17h. 

 , 21h. 

 , Ih. 



1,984,200 

 235,400 

 337,000 



2,305,100 

 455,600 



6,819,000 



Thus, in respect to the distribution of stars of different 

 magnitudes in the heavens, we perceive that the least 

 crowded regions lie between nine and seventeen hours, 

 and twenty-one, and five hours of right ascension. If we 

 take the most brilliant stars, or those of the three first 

 magnitudes only into account, we find them to be pretty 

 evenly distributed over the surface of the heavens ; but 

 those of the fourth, fifth, and sixth magnitudes are con- 

 gregated more densely as they approach the Milky Way. 

 At every succeeding class this becomes more and more 

 apparent, and the faintest stars are most thickly crowded 

 in and near this zone. This would naturally lead us to 

 imagine that there is some connection between the great 

 galactic circle and the other portions of the heavens, 

 and that they might form one great system. 



The Milky Way extends completely round the heavens, 

 and makes almost a great circle upon its surface. The 

 breadth is very unequal : in some regions it is not more 

 than 6; in other parts it is two or three times that 

 breadth. For one-third of its extent, viz., between Ser- 

 pentarius and Antinous, it is divided into two branches ; 

 but for this distance of about 120, the dark opening is 

 of no great breadth. The resolvability of the Milky 

 Way into distinct individual stars, which was proved im- 

 mediately on the invention of the telescope, had been 

 long previously conjectured by some of the ancient philo- 

 sophers ; whilst the absurd suppositions of others on its 

 structure if they were ever supposed worthy of exami- 

 nation were dissipated by the same discovery. No 

 other theory was started, however, to supply their place, 

 or to explain this phenomenon, until about the middle 

 of the eighteenth century, when Thomas Wright, of 

 Durham, author of the Clavis Ccelestis, endeavoured, in 

 his Theory of the Universe, to account for this appear- 

 ance, by supposing that the stars were ranged in regular 

 strata, and not dispersed fortuitously throughout space, 

 as was previously supposed. By this arrangement, 

 although the individual stars composing the stratum 

 were at vast distances apart, yet, supposing our sun and 

 its attendant satellites to be situated near the centre of 

 this plane, we should witness such an appearance as the 

 Milky Way presents. In the direction of the plane, the 

 stars would be seen in such vast numbers, although the 

 more distant ones would be so extremely small, that it 

 would appear as a white and confused zone of light pro- 

 jected on the dark space surrounding us on every side. 

 This idea received further development from the cele- 

 brated Immanuel Kant, who considered that it was 

 rendered probable, from the arrangement of the three 

 or four thousand stars visible to the naked eye, the 

 greater number of which were contained in a zone within 

 a short distance of the galactic circle. Lambert was 

 likewise of opinion, that all the stars visible through the 

 best telescopes lay in one vast stratum ; but he considered 

 that many of the clusters in the Milky Way were sepa- 

 rate and individual systems, but nevertheless subsidiary 

 members of one great system. Those immense clusters, 

 each containing millions of stars, were connected anil 

 held together by the same power which predominates in 



