Rudiments of Natural Philosophy and Astronomy (Google eBook)

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E.D. Truman, 1852 - Astronomy - 115 pages
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Page 57 - In any year, the number of eclipses of both luminaries cannot be less than two, nor more than seven. The most usual number is four, and it is very rare to have more than six.
Page 113 - ... suppose that we can enter into them to any but a very small degree. They doubtless go immeasurably beyond our mode of understanding or conceiving them. But to a certain extent we can go. We can go so far as to see that they are Ends and Purposes. It is not a vain presumption in us to suppose that we know that the eye was made for seeing and the ear for hearing.
Page 103 - ... of the same fluid, the pressure of the atmosphere is wholly removed from the upper surface of the mercury in the tube, while it continues to act on the mercury in the bason, and by its means on the lower surface of the column in the tube.
Page 57 - ... the sum of the apparent semi-diameters of the sun and moon. When within these limits, it is a problem of numbers and of spherical trigonometry to ascertain the nature of the eclipse, if any, which will happen, The number of eclipses of the sun and moon together in a year cannot be less than two, or more than seven; the most usual number is four, and it is rare to have more than six. The explanation of the limitation of the number of E.
Page 37 - ... millions of miles. No human mind can comprehend fully what this vast distance means. But we may form some conception of it by such an illustration as this : A ship may leave Liverpool and cross the Atlantic to New York after twenty days...
Page 94 - This law is expressed by saying, that the volume of a given weight of air is inversely as the, compressing force.
Page 59 - The cause of the. tides is the unequal attraction of the sun and moon upon different parts of the earth. . For they attract the parts of the earth's surface nearest to them, with a greater force than they do its centre : and attract the centre more than they do the opposite surface. To restore this equilibrium the waters take a spheroidal figure, whose longer axis is directed towards the attracting luminary.
Page 51 - The center of gravity of a body is a certain point about which all parts of the body balance each other, so that when that point is supported, the whole body is supported.
Page 17 - It appears to be about one third of the way from the horizon to the zenith ; then its altitude is 30 degrees.
Page 47 - ... bodies, it must decrease, as the square of the distance from the centre of the earth increases ; that is, at double the distance, it would be four times less ; at ten times the distance, one hundred times less ; and so on. Now, it was known that the moon is about sixty times as far from the centre of the earth as the surface of the earth is from the centre, and consequently, the force of attraction at the moon must be the square of sixty, or thirty-six hundred times less than it is at the earth...

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