ALAXY, in astronomy. A very re malkable appearance in the heavens is that called the galaxy, or the milky-way. This is a broad circle, sometimes dou ble, but for the most part single, sur rounding the whole celestial concave. We perceive also in different parts of the heavens small white spots, which ap pear to be of the same nature with the milky-way. These spots are called ne bulx.
With a powerful telescope, Dr. Her schel first began to survey the via lactea, and found that it completely resolved the whitish appearance into stars, which the telescope he formerly used had not power enough to do. The portion he first ob served was that about the hand and club of Orion ; and found therein an astonish ing multitude of stars, whose number he endeavoured to estimate, by counting many fields, and computing from a mean of these how many might be contained in a given portion of the milky-way. In the most vacant place to be met with in that neighbourhood, he found 63 stars ; other six fields contained 110, 60, 70, 90, 70, and 74 stars ; a mean of all which gave 79 for the number of stars to each field ; and thus he found, that by allowing 15 minutes for the diameter of his field of view, a belt of 15 degress long and two broad, which he had often seen pass be fore his telescope in an hour's time, could not contain less than 50,000 stars, large enough to be distinctly numbered ; be sides which, he suspected twice as many more, which could be seen only now and then by faint glimpses, for want of suffi cient light. The success he had within the milky-way soon induced him to turn his telescope to the nebulous parts of the heavens, of with an accurate list had been published in the " Connoisance des Temps, for 1783 and 1784." Most of these yielded to a Newtonian reflector, of 20 feet focal distance, and 12 inches aperture , which plainly discovered them to be composed of stars, or at least to contain stars, and to show every other indication of its consisting of them en tirely.
" The nebula (says he) are arranged in strata, and run on to a great length, and some of them I have been able to pursue, and to guess pretty well at their form and direction. It is probable enough that they may surround the whole starry sphere of the heavens, not unlike the milky-way, which undoubtedly is nothing but a stratum of fixed stars : and as this latter immense starry bed is not of equal breadth or lustre in every part, nor runs on in one straight direction, but is curv ed, and even divided into two streams along a very considerable portion of it, we may likewise expect the greatest va riety in the strata of the cluster of stars and nebulae. One of these nebulous beds
is so rich, that in passing through a sec tion of it in the time of only 36 minutes, I have detected no less than 31 nebula, all distinctly visible upon a fine blue sky. Their situation and shape, as well as con dition, seem to denote the greatest va riety imaginable. In another stratum, or perhaps a different branch of the former, I have often seen double and treble ne bula variously arranged ; large ones, with small seeming attendants ; narrow, but much extended lucid nebulae or bright dashes ; some of the shape of a fan, re sembling an electric brush issuing from a lucid point ; others of the emetic shape, with a seeming nucleus in the centre, or like cloudy stars, surrounded with a ne bulous atmosphere a different sort, again, contain a nebulosity of the milky kind, like that wonderful inexplicable phenomenon about Orion is ; while others shine with a fainter mottled kind of light, which denotes their being resolvable into stars.
" It is very probable that the great stratum, called the milky-way, is that in which the sun is placed, though perhaps not in the very centre of its thickness. We gather this from the appearance of the galaxy, which seems to encompass the whole heavens as it certainly must do, if the sun is within the same ; for, sup pose a number of stars arranged between two parallel planes, indefinitely extended every way, but at a given considerable distance from one another, and calling this a sideral stratum, an eye placed somewhere within it will see all the stars in the direction of the planes of the stra tum projected into a great circle, which will appear lucid, on account of the accu mulation of the stars, while the rest of the heavens, at the sides, will only seem to be scattered over with constellations, more or less crowded, according to the distance of the planes, or number of stars, contained in the thickness or sides of the stratum."