Elementary Treatise on Astronomy

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J. Wiley, 1852 - Astronomy - 510 pages
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Page 380 - Way, and clustering groups sufficiently insulated and condensed to come under the designation of irregular, and in some cases pretty rich clusters. But besides those, there are also nebulae in abundance, both regular and irregular ; globular clusters in every state of condensation; and objects of a nebulous character quite peculiar, and which have no analogue in any other region of the heavens.
Page 161 - Ranges of mountains, extending in length two or three hundred miles. These ranges bear a distant resemblance to our Alps, Apennines, and Andes, but they are much less in extent, and do not form a very prominent feature of the lunar surface. Some of them appear very rugged and precipitous, and the highest ranges are, in some places, above four miles in perpendicular altitude. In some instances they run nearly in a straight line from northeast to southwest, as in that range called the Apennines ; in...
Page 381 - Throughout by far the larger portion of the extent of the Milk-y Way in both hemispheres, the general blackness of the ground of the heavens on which its stars are projected, and the absence of that innumerable multitude and excessive crowding of the smallest visible magnitudes, and of glare produced by the aggregate light of multitudes too small to affect the eye singly, which the contrary supposition would appear to necessitate, must, we think, be considered unequivocal indications that its dimensions...
Page 380 - ... we could plainly see that all about the trapezium is a mass of stars ; the rest of the nebula also abounding with stars and exhibiting the characteristics of resolvability strongly marked.
Page 197 - ... them, render it extremely probable that they subsist in the atmosphere of the planet, forming tracts of comparatively clear sky, determined by currents analogous to our trade-winds, but of a much more steady and decided character, as might indeed be expected from the immense velocity of its rotation. That it is the comparatively darker body of the planet which appears in the belts is evident from this, — that they do not come up in all their strength to the edge of the disc, but fade away gradually...
Page 161 - Insulated mountains, which rise from plains nearly level, like a sugar loaf placed on a table, and which may be supposed to present an appearance somewhat similar to Mount Etna or the peak of Teneriffe. The shadows of these mountains, in certain phases of the moon, are as distinctly perceived as the shadow of an upright staff when placed opposite to the sun ; and their heights can be calculated from the length of their shadows.
Page 20 - LONGITUDE of a place, in geography, is an arch of the equator, intercepted between the first meridian and the meridian passing through the...
Page 30 - ... or 7% 7, &c. according to its apparent relative distance from the wire. This kind of observation must be made at each of the five wires, and a mean of the whole taken, which will represent the time of the star's passage over the mean or meridional wire. The utility of having five wires instead of the central one only, will be readily understood, from the consideration that a mean result of several observations is deserving of more confidence than a single one ; since the chances are, that an...
Page 26 - TT is a telescope formed of two parts, connected by a spherical center-piece, into which are fitted the larger ends of two cones, the common axis of which is placed at right angles to the axis of the telescope, to serve as the horizontal axis of the instrument. The two small ends of these cones are ground into two perfectly equal cylinders, called pivots. The pivots rest upon angular bearings or Ys.
Page 27 - ... horizontal, the other vertical, so that, by means of screws, one end of the axis may be pushed a little forwards or backwards, and the other end may be either slightly depressed or elevated. Which two small* movements are necessary, as it will be soon explained, for two adjustments of the telescope. Let E be called the eastern pillar, W the western. On the eastern end of the axis is fixed (so that it revolves with the axis) an index n, the upper part of which, when the telescope revolves, nearly...

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