Popular Astronomy: A Series of Lectures

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Macmillan and Company, 1866 - Astronomy - 292 pages

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Page 229 - Every particle of matter attracts every other particle of matter with a stress which is proportional to the product of their masses, and inversely as the square of the distance between them.
Page 126 - The squares of the times of revolution of any two planets are to each other, in the same proportion as the cubes of their mean distances from the sun.
Page 128 - With the latter supposition (in which the distances are in the same proportion as in the former) we should find that Venus will appear to go just as much to the right or to the left of the sun as with the former. And therefore when we find that the apparent motions, computed on the supposition that the distances of the earth and Venus from the sun are respectively one hundred and seventy-two millions of miles, do agree with those which are really observed, we cannot tell whether the real distances...
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 260 - Dr. Reich ; and finally, in a very much more complete way, by Mr. Francis Baily, as the active member of a committee of the Astronomical Society of London, to whom funds were supplied by the British Government. It is an experiment of a different kind ; a sort of domestic experiment ; one of those experiments which can be made in your own observing rooms at home, and which are, in many respects, preferable to those made on the hill sides of Scotland. The shape in which the apparatus is represented...
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.
Page 13 - ... is certain. Having now come to that result, as one which is generally established, I shall just mention a slight departure from it. Perhaps you may be surprised to hear me say the rule is established as true, and yet there is a departure from it. This is the way we go on in science, as in everything else...
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 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...

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