, or Milky-Way, or Via Lactea, in Astronomy, that long, whitish, luminous track, which seems to encompass the heavens like a swath, scarf, or girdle; and which is easily seen in a clear night, especially when the moon is not up. It is of a considerable, though unequal breadth; being also in some parts double, but in others single.

The Galaxy passes through many of the constellations in its circuit round the heavens, and keeps its exact place or position with respect to them.

There have been various strange and fabulous stories and opinions concerning the Galaxy.

The ancient poets, and even some of the philosophers, speak of it as the road or way by which the heroes went to heaven. But the Egyptians called it the Way of Straw, from the story of its rising from burning straw, thrown behind the goddess Isis in her flight from the giant Typhon. While the Greeks, who affect to derive every thing in the heavens from some of their own fables, have two origins for it; the one, that Juno, without perceiving it, accidentally gave suck to Mercury when an infant, but that as soon as she turned her eyes upon him, she threw him from her, and as the nipple was drawn from his mouth, the milk ran about for a moment; and the other, that the infant Hercules being laid by the side of Juno when asleep, on waking she gave him the breast; but soon perceiving who it was, she threw him from her, and the heavens were marked by the wasted milk.

Some other philosophers however gave it a different turn, and different origin: these esteemed it to be a tract of liquid fire, spread in this manner along the skies: and others again, supposing a celestial region beyond all that was visible, and imagining that fire, at some time let loose from thence, was to consume the world, made this a part of that celestial fire, and appealed to it as a presage of what would surely happen. This diffused brightness they considered as a crack in the vault or wall of heaven, and fancied this a glimmering of the celestial fire through it, and that there required nothing more than the undoing of this| crack by some accident in nature, or by the will of the Gods, to make the whole frame start, and let out the fire of destruction.

Aristotle makes the Galaxy a kind of meteor, formed of a crowd of vapours, drawn into that part by certain large stars disposed in the region of the heavens answering to it. Others, finding that the Galaxy was seen all over the globe, that it always corresponded to the same fixed stars, and that it was far above the highest planets, set Aristotle's opinion aside, and placed the Galaxy in the sirmament or region of the fixed stars; and concluded that it was nothing else but an assemblage of an infinite number of minute stars. And since the invention of telescopes, this opinion has been abundantly confirmed. For, by directing a good telescope to any part of the milky way, we perceive an innumerable multitude of very small stars, where before we only observed a confused whiteness, arising from the assemblage and union of their joint light; like as any thing powdered with fine white powder, at a distance we only observe the confused whiteness, but on examining it very near we perceive all the small particles of the powder separately; as Milton finely expresses it, A broad and ample road, whose dust is gold, And pavement stars, as stars to thee appear, Seen in the Galaxy, that milky way, Which nightly, as a circling Zone thou seest Powder'd with stars.

There are other such marks in the heavens; as the nebulæ, or, nebulous stars, and certain whitish parts about the south pole, called Magellanic clouds, which are all of the same nature, appearing to be vast clusters of small stars when viewed through a telescope, which are too faint to affect the eye singly.

M. le Monnier however, not being able to discover more stars in this space than in other parts of the heavens, disputes the opinion above recited as to the reason of the whiteness, and supposes that this and the nebulous stars are occasioned by some other kind of matter. Inst. Ast. p. 60.

GALILEI (Galileo,) a most excellent philosopher, mathematician and astronomer, was born at Pisa in Italy, in 1564. From his infancy he had a strong propensity to philosophy and mathematics, and soon made a great progress in these sciences. So that in 1592 he was chosen professor of mathematics at Padua. While he was professor there, visiting Venice, then famous for the art of glass-making, he heard that in Holland a glass had been invented, through which very distant objects were seen distinctly as if near at hand. This was sufficient for Galileo; his curiosity was raised, and put him upon considering what must be the form of such a glass, and the manner of making it. The result of his enquiry was the invention of the telescope, produced from this hint, without having seen the Dutch glass. All the discoveries he made in astronomy were easy and natural consequences of this invention, which opening a way, till then unknown, into the heavens, thence brought the finest discoveries. One of the first of these, was that of 4 of Jupiter's satellites, which he called the Medicean stars or planets, in honour of Cosmo the 2d, grand-duke of Tuscany, who was of that family. Cosmo sent for our astronomer from Padua, and made him professor of mathematics at Pisa in 1611; and soon after inviting him to Florence, gave him the office and title of principal philosopher and mathematician to his highness.

He had been but a few years at Florence, before the Inquisition began to be very busy with him. Having observed some solar spots in 1612, he printed that discovery the following year at Rome; in which, and in some other pieces, he ventured to assert the truth of the Copernican system, and brought several new arguments to confirm it. For these he was cited before the Inquisition at Rome, in 1615: after some months imprisonment, he was released, and sentence pronounced against him, that he should renounce his heretical opinions, and not defend them by word or writing, or insinuate them into the minds of any persons. But having afterwards, in 1632, published at Florence his Dialogues of the two Great Systems of the World, the Ptolomaic and Copernican, he was again cited before the holy-office, and committed to the prison of that ecclesiastical court at Rome. The inquisitors convened in June that year; and in his presence pronounced sentence against him and his books, obliging him to abjure his errors in the most solemn manner; committed him to the prison of their office during pleasure; and enjoined him, as a saving penance, for three years to come, to repeat once a week the seven penitential psalms: reserving to themselves, however, the power of moderating, changing, or taking away altogether or in part, the said punishment and penance. On this sentence, he was detained in prison till 1634; and his Dialogues of the System of the World were burnt at Rome.

Galileo lived ten years after this; seven of which were employed in making still further discoveries with his telescope. But by the continual application to that instrument, added to the damage his sight received from the nocturnal air, his eyes grew gradually weaker, till he became totally blind in 1639. He bore this calamity with patience and resignation, worthy of a great philosopher. The loss neither broke his spirit, nor stopped the course of his studies. He supplied the defect by constant meditation; by which means he prepared a large quantity of materials, and began to arrange them by dictating his ideas; when, by a distemper of three months continuance, wasting away by degrees, he expired at Arcetri near Florence, in January 1642, being the 78th year of his age.

Galileo was in his person of small stature, though of a venerable aspect, and vigorous constitution. His conversation was affable and free, and full of pleasantry. He took great delight in architecture and painting, and designed extremely well. He played exquisitely on the lute; and whenever he spent any time in the country, he took great pleasure in husbandry. His learning was very extensive; and he possessed in a high degree a clearness and acuteness of wit. From the time of Archimedes, nothing had been done in mechanical geometry, till Galileo, who being possessed of an excellent judgment, and great skill in the most abstruse points of geometry, first extended the boundaries of that science, and began to reduce the resistance of solid| bodies to its laws. Besides applying geometry to the doctrine of motion, by which philosophy became established on a sure foundation, he made surprising discoveries in the heavens by means of his telescope. He made the evidence of the Copernican system more sensible, when he shewed from the phases of Venus, like to those of the moon, that Venus actually revolves about the sun. He proved the rotation of the sun on his axis, from his spots; and thence the diurnal rotation of the earth became more credible. The satellites that attend Jupiter in his revolution about the sun, represented, in Jupiter's smaller system, a just image of the great solar system: and rendered it more easy to conceive how the moon might attend the earth, as a satellite, in her annual revolution. By discovering hills and cavities in the moon, and spots in the sun constantly varying, he shewed that there was not so great a difference between the celestial bodies and the earth as had been vainly imagined.

He rendered no less service to science by treating, in a clear and geometrical manner, the doctrine of motion, which has justly been called the key of nature. The rational part of mechanics had been so much neglected, that hardly any improvement was made in it for almost 2000 years. But Galileo has given us fully the theory of equable motion<*>, and of such as are uniformly accelerated or retarded, and of these two compounded together. He, first of any, demonstrated that the spaces described by heavy bodies, from the beginning of their descent, are as the squares of the times; and that a body, projected in any direction not perpendicular to the horizon, describes a parabola. These were the beginnings of the doctrine of the motion of heavy bodies, which has been since carried to so great a height by Newton. In geometry, he invented the cycloid, or trochoid; though the properties of it were afterwards chiefly demonstrated by his pupil Torricelli. He invented the simple pendulum, and made use of it in his astronomical experiments: he had also thoughts of applying it to clocks; but did not execute that design: the glory of that invention was reserved for his son Vicenzio, who made the experiment at Venice in 1649; and Huygens afterward carried this invention to perfection. Of Galileo's invention also, was the machine, with which the Venetians render their Laguna fluid and navigable. He also discovered the gravíty of the air, and endeavoured to compare it with that of water; besides, opening up several other enquiries in natural philosophy. In short, he was not esteemed and followed by philosophers only, but was honoured by persons of the greatest distinction of all nations.

Galileo had scholars too that were worthy of so great a master, by whom the gravitation of the atmosphere was fully established, and its varying pressure accurately and conveniently measured, by the column of quicksilver of equal weight sustained by it in the barometrical tube. The elasticity of the air, by which it perpetually endeavours to expand itself, and, while it admits of condensation, resists in proportion to its density, was a phenomenon of a new kind (the common fluids having no such property), and was of the utmost importance to philosophy. These principles opened a vast <*>eld of new and useful knowledge, and explained a great variety of phenomena, which had been accounted for before that time in a very absurd manner. It seemed as if the air, the fluid in which men lived from the beginning, had been then but first discovered. Philosophers were every where busy enquiring into its various properties and their effects: and valuable discoveries rewarded their industry. Of the great number who distinguished themselves on this occasion, may be mentioned Torricelli and Viviani in Italy, Pascal in France, Otto Guerick in Germany, and Boyle in England.

Galileo wrote a number of treatises, many of which were published in his life-time. Most of them were also collected after his death, and published by Mendessi in 2 vols 4to, under the title-of L'Opere di Galileo Galilei Lynceo, in 1656. Some of these, with others of his pieces, were translated into English and published by Thomas Salisbury, in his Mathematical Collections, in 2 vols folio. A volume also of his letters to several learned men, and solutions of several problems, were printed at Bologna in 4to. His last disciple, Vincenzo Viviani, who proved a very eminent mathematician, methodized a piece of his master's, and published it under this title, Quinto libro de gli Elententi d'Euclidi, &c; at Florence in 1674, 4to. Viviani published some more of Galileo's things, being Extracts from his letters to a learned Frenchman, where he gives an account of the works which he intended to have published, and a passage from a letter of Galileo dated at Arcetri, Oct. 30, 1635, to John Camillo, a mathematician of Naples, concerning the angle of contact. Besides all these, he wrote many other pieces, which were unfortunately lost through his wife's devotion; who, solicited by her confessor, gave him leave to peruse her husband's manuscripts; of which he tore and took away as many as he said were not sit to be published.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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