A Popular Astronomy: A Series of Lectures

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Macmillan and Company, 1866 - Astronomy - 292 pages
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Page 11 - Everybody knows well that whirling these balls round by the rotation of the axis CD, to which they are attached, causes them to spread out. When the speed has reached a certain limit, the spreading out of these brings the moving parts, as at E and F, into contact with the fixed parts GH, and produces a degree of friction which prevents further acceleration; and thus a uniform speed is produced, with very great nicety. This contrivance is in constant use on my Equatoreal at the present time. You will...
Page 229 - But if it is true that every particle of matter attracts every other particle of matter, with a force varying inversely as the square of the distance...
Page ix - This worh consists of six lectures, which are intended " to explain to intelligent persons the principles on which the instruments of an Observatory are constructed (omitting all details, so far as they are merely subsidiary), and the principles on which the observations made with these instruments are treated for deduction of the distances and weights of the bodies of the Solar System, and of a fftv stars, omitliitt' all minntice of Elementary Class-Books — continued. formulce, and all troublesome...
Page 286 - Electricity is usually developed, in order to show its effects, by the friction of glass. The earlier electricians, in the prosecution of their researches, merely used glass tubes or other nonconductors, held in one hand and...
Page 187 - Now the sun attracts the moon, and disturbs it as he would the path of the mountain we have just supposed, and the effect is the same — viz., the intersections of the moon's orbit with the ecliptic travel backward, completing a revolution in about 18 years. During half of this time the moon's orbit is inclined to the ecliptic in the same way as the earth's equator ; during the other half it is inclined in the opposite way. In the former state, the moon's attractive tendency to tilt the earth is...
Page 131 - In nature we do not know any instance of the hyperbola ; comets, as we shall see hereafter, for the most part move in parabolas ; some comets and all the planets move in ellipses ; and some of these ellipses approach very nearly to circles. I am exceedingly sorry that it is impossible for me to give you an idea of the steps of these investigations ; but I say, and I am sure you will agree with me, that half a man's life would be well spent in mastering them. Kepler's third law is this : that if we...
Page 242 - He assumed the earth to be fluid, or at least to be so far fluid in all parts below the surface that its form would be the same as if it were entirely fluid. This fluid matter he assumed to be equally dense in every part, so that it was composed of no heavier matter at the centre than at the circumference. For trial of his theory he supposed the fluid earth to be a spheroid ; he then computed the attraction of the whole spheroid upon every one of its component particles of fluid; with this he combined...
Page 114 - ... manner as I can what parallax is. There is an experiment pleasing and profitable, and which I have made in my youth, and which I have no doubt most of you have made in your time. It is this : if you place your head in...
Page 196 - In the southern hemisphere, there is the bright star of the Centaur, (Alpha Centauri,) for which it would seem that the inclination of the two lines from the opposite sides of the earth's orbit to the star, is an angle of two seconds and no more. An angle of two seconds is that in which a circle ^ of an inch in diameter would be seen at the distance of a mile.
Page 287 - ... a mine be found, the ratio of the force of gravity at the top to that at the bottom may be calculated, and thence the ratio of the mean density of the earth to that of its surface.

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