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niSTORY OF PHYSICAL ASTRONOMY.

of research. To attempt to discover the mechanical structure of morecomplicated systems, before observations were amassed capable of forminga sure groundwork of research, would be manifestly a hopeless under-taking. All speculations directed to this end must therefore be regardedas premature, in the present state of sidereal astronomy*.

The remarkable Zone of light termed the Milky Way , which is seenencircling the starry heavens, has in all ages excited the admiration ofmankind, and stimulated the enquiries of the contemplative observer ofnature. It would serve no useful purpose to refer here to the erroneousopinions entertained by various ancient philosophers respecting the natureof this luminous circle. Aristotle supposed it to be composed of a sub-stance occupying an intermediate position between the terrestrial atmo-sphere and the region of the stars. In no part of his great work hasPtolemy expressed an opinion respecting the nature of the Milky Way .It is a remarkable fact, however, that Democritus hit upon the true ex-planation of its aspect. According to Plutarch , he maintained that itwas composed of a multitude of small stars, so very near to each other,that their light became blended together so as to produce the appearanceof a luminous zonef. A similar opinion respecting the Milky Way isexpressed by Mauilius, in his poem on the sphere t.

Copernicus has cautiously abstained from any allusion to the MilkyWay , in his immortal work wherein he expounds the true system of theuniverse. Tycho Brahe supposed it to be formed of a nebulous sub-stance, as is evident from his speculations on the origin of the new starwhich appeared in the year 1572§. A similar view of its structure wasimplied in Kepler’s speculations on the origin of the new star of 1004 [|.

The invention of the telescope, about the beginning of the seventeenthcentury, had the effect of conducting astronomers to a more accurateknowledge respecting the constitution of the Milky Way than had hithertoprevailed. When Galileo first explored the heavens with his telescope,he discovered everywhere, to his unspeakable admiration, a multitude ofstars which were too faint to be perceived with the naked eye. Theaspect of the Milky Way was found by him to arise wholly from its beingcomposed of a vast collection of small stars in close proximity to oneanother. In the Sidereus Nuncius , a small work containing the firstannouncement of his telescopic discoveries in the heavens, he congratu-lates himself on having put an end to the ancient controversy respectingthe Milky Way , by actually exhibiting its structure to the senses If.Thenceforward it has been generally admitted, that the Milky Way is, infact, no other than a vast assemblage of stars too small to be individuallyvisible.

* Among those who have partially laboured on the subject of nebulae, no one exhi-bited such high qualifications for cultivating so delicate a branch of stellar astronomy asEbenezer Porter Mason, a young American of great promise, who unfortunately died inthe year 1840, at tire early age of twenty-one years. An important paper, containing theresults of his observations of some remarkable nebulae, is inserted in vol. vii. of theTransactions of the American Philosophical Society. There is a very interesting ac-count of the life and writings of this true son of genius, written by Professor Olmsted,of Yale College, Connecticut. (12mo, New York , 1842.)

■f De Plaeit. lib. iii., cap. i.

$ “ An major densa stellarum turba corona

Contexit flammas, et crasso lumine eandet,

Et fulgore nitet collato ciarior orbis.”—I.ib. i., cap. ix.

§ Progymnasmata, p. 795. || “ De Stella Nova,” cap. xxiii,, p. 115.

•fl Opere di Galileo, tome ii., p. 4.