The Milky Way may be described in general terms as extending three or four degrees on each side of a great circle inclined at an angle of about CO' to the ecliptic, which it cuts in the northern hemisphere between the horns of Taurus and the feet of Gemini, and in the southern hemisphere between Sagittarius and Scorpio. Beginning with the part nearest to the North Pole, it nearly covers Cassiopeia and Perseus, and then, becoming thinner, pessee through Auriga, between Taurus and Gemini, and near the back of Canis Major through Argo. It then narrows considerably, and passing under the hind feet of Cen taurus, widens again near Ara. A little above the last constellation, and before it again meets the ecliptic, it divides into the two streams above mentioned, which contain between them a long thin strip passing through part of Scorpio, Serpens, Aquila, Vulpocula, and Cygnus. In Cygnus the streams reunite, but inunediately separate again, finally reuniting higher up in the same constellation, from whence the main stream reaches Cassiopeia, &c.
Sir John Herschel, in his Results of Astronomical Observations made during the years 1834.5-6-7-8, at the Cape of Good Hope,' 4to., 1847. has some valuable remarks on the general appearance and tele scopic constitution of the Milky Way in the southern hemisphere ; and has also given'an accurate delineation of that portion of it which extends from the constellation Antinoos through Centaurus to Morioceros.
The Milky Way was called by the Greeks Tae-F(-r, (whence our word Celery), or sc6nAos 7aAeuerixOs, and by the Romans Orbit lacicus. The mythology of the former people on the subject is as edifying as usual : Hyginus fixes on Eratosthcnes the most common story, namely, that the Galaxy arose from the milk of Juno, who pushed Hercules away from her breast (where lie had been placed by Jupiter) on learning that he was the son of Main. Nor does the above accurate writer forget to mention that others held the appearance to have arisen from young master Hercules having been a greedy child, and having filled his mouth too full. Others thought that the whole was not milk, but ears of corn which Isis dropped in her flight from Typhon. Another fable, mentioned by Plato, makes tiro Milky Way to be a breed causeway through the heavens for gods and heroes to walk upon; another, that it is the part of the heaven which was singed when the horses of the sun ran away with I'haeton. These stories are a proper prelude to the speculations of the philosophers width followed. Some of the Pythagoreans are reported to have supposed the Milky Way to be an old tied disused path of the sun, out of which, some said, he was frightened by the banquet of Thyestes ; others, a reflection from the sun. Anaxaguras is said to have thought it was the shadow of the earth : Aristotle supposed it to be sublunary, and to consist of ex halations, of the same matter as comets. Poaidonius took it for a band
of fire; Theophrastus for a solid and luminous band, joining together the two hemispheres; while Diodorus thought it was celestial fire shining through the clefts of the solid heavens. Democritus hit the true explanation, namely, that it is a congeries of little stars to small to be separately seen—an opinion which both Plutarch (' De I'lacit.
L iLL, c. 1) and Manilina mention. Shortly after the invention of the telescope, Galileo announced that he had resolved the whole of the Milky Way into stars. " Eat enim Gala.ria nihil aliud quam bone win-arum suph,rum coacerratim conaiturum congeries: in quainctinque cnim regionom illiva perepicillum dirigas, mtatim stellarnin ingens frequentin stye in conspectum protest quarum complures sada Inagua) ct valde conspicum videntur, std exiguarum multitude pronaua inex plorabilis tat." Nuncius Sidereue.') It is however not easy to sup peee that Galileo's resolution of the Milky Way was complete; and we rimy here see bow necessary is attention to minute destription. When Sir J. Herschel, in the paragraph cited above, states the stars to appear " like glittering dust on the black ground of the general hearens," we know that, if the observer can be depended upon, he has completely received the continuous light in question : but if be only says, with Galileo, that he detected innumerable stars, we are only sure that he has distinguished the nearer stars, and may suppose that the more distant ones still formed a Milky Way behind them. That this must have been the ease with Galileo (whose telescopes would never dis tinctly show Satorn's ring) may be confidently asserted. It must also be remembered that Galileo had completely resolved several nobuln, and might easily have completed his assertion as to the Milky Way from analogy. Kepler (' Dioptr. Pref.') describes this resolution in a way which will be some guide as to its character : "Nebuloss atella ostendit, ut in Via LactoA, dims, tres, vel quatuor chuissitnas fityllas in orctissimo spatio collocatas;" that two, three, or four stars were seen in the smallest space : this may very well correspond to Sir W. if embers estimate of 50,000 in the zone above mentioned, without the necessity of summing that those stars were seen, which the forty foot reflector would only show by glimpses. Sir W. Herschel counted seventy-nine stars, on the average, in a field of fifteen minutes in diameter, showing about as much of the heavens as is covered by one fourth part of the moon. If, which may be suspected, tho " arctissi mum apatium" of Kepler meant the field of his telescope, the resolu tion thus obtained would not quite justify the conclusion, except as a probable deduction ; the real and necessary inference would only have been, that stars invisible to the naked eye exist in every part of the Milby Way in considerable numbers.