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HISTORY OF PHYSICAL ASTRONOMY.

the beginning of the seventeenth century, by removing the veil which hadso long concealed those remote orbs from the scrutinies of the humanmind, gave an unexpected impulse to researches of this nature. Fromthe epoch of Galileo’s brilliant discoveries in the celestial regions, maybe said to date the origin of Stellar Astronomy, a branch of enquiry whichhas ever since attracted more or less attention, and which, in recent timesespecially, has excited an intense degree of interest.

That the stars are so many suns shining by their own light, is anopinion which seems to have been entertained by some of the ancientphilosophers. This view of their nature came to be universally adoptedupon the establishment of the true system of the world by Copernicus ,since it was considered to be improbable in the highest degree, that bodiesshining by reflected light would be visible at the earth, when at the sametime their distance was so immense, that they did not exhibit any sensiblechange of position even when viewed at the opposite extremities of adiameter of the terrestrial orbit.

The number of stars visible to the naked eye, is found to amount onlyto a few thousands; for although at first sight they seem to be innume-rable, yet a closer scrutiny of the heavens soon serves to convince theobserver that he has been labouring under a delusion in this respect.But wliat the unaided organ of vision merely suggests to the imagina-tion, without affording any substantial grounds of belief in its existence,an examination of the starry heavens with the telescope lias proved to bea reality. Multitudes of stars are then perceived, which were invisible tothe naked eye. The number also thus disclosed to view, continuallyaugments with each successive increase of the optical power of the in-strument, until the imagination is at length absolutely overwhelmed withthe countless myriads of suns, and systems of suns, which are found topeople the immensity of space.

The ancient philosophers supposed the celestial bodies to be essentiallyincorruptible and eternal, and hence maintained that they were not sub-ject to physical changes, as in the case of bodies at the surface of theearth. The progress of astronomical science, however, has served amplyto demonstrate that those brilliant orbs are not exempt from the greatlaw of mutation, to which all the other objects of the created universeappear to be liable. Exclusively of the evidence afforded by the observa-tions of astronomers on the physical constitution of the sun, there arevarious stellar phenomena of a highly-interesting nature, which concur inestablishing this important faet, A brief allusion to some of them maynot perhaps be unacceptable to the reader.

In some instances, stars which have shone for ages in the firmament,have ceased to be visible. A comparison of catalogues of the stars con-structed for different epochs, would indeed seem to iudicate that a greatnumber of such objects that were formerly visible in the celestialsphere, have totally vanished; but it is probable that in most of thesecases the discordance is attributable to the imperfection of the earlierobservations of astronomers. Stars, hov'ever, have been mentioned byMontanan*, Maraldi j, and Sir William Herschelj, respecting whose ex-tinction there hardly exist grounds for entertaining any reasonabledoubt.

* Phil. Trans., 1071, p. 2202. f Mem. Acad, des Sciences, 1709, p. 40.

t PhiL Trans., 1792, p. 26.