# An Essay on the Use of the Spirit Level: As Applied to Engineering and Other Purposes

T. and J. Hodgson and sold by E. Charnley, 1838 - Leveling - 106 pages

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Page 11 - If from any point without a circle two straight lines be drawn, one of which cuts the circle, and the other touches it ; the rectangle contained by the whole line which cuts the circle, and the part of it without the circle, is equal to the square of the line which touches it.
Page 13 - In any right-angled triangle, the square which is described upon the side subtending the right angle, is equal to the squares described upon the sides which contain the right angle.
Page 11 - IF from any point without a circle two straight lines be drawn, one of which cuts the circle, and the other touches it ; the rectangle contained by the whole line which cuts the circle, and the part of it without the circle, shall be equal to the square of the line which touches it.
Page 56 - When the latitudes are both of the same name, that is, both North or both South, subtract the less from the greater, and the remainder will be the difference of latitude. But when one is North, and the other South, their sum will be the difference of latitude.
Page 66 - FOR THE FIRST PART Cipher• a, b, c, d, e, f, g, h, i, j, k, 1, m, n, o, p, q, r, s, t, u, v, w, x, y, z. Key. z, y, x, w, v, u, t, s, r, q, p, o, n, m, 1, k, j, i, h, g, f, e, d, c, b, a. In the second part of the work, a totally different system is employed. The words may be deciphered by taking the last letter, then the first, then the last but one, then the second, and so on. Two or three words are also often run into one; for example ereetemhdrdoh, is he ordered them. The nine...
Page 35 - ... ruler wherein it is fixed is level. When it is not level, the bubble will rife to one end. Thi...
Page 19 - But as the operation of retraction incurvating the rays of light proceeding from objects near the horizon is considerable, it can by no means be neglected, when the difference between the true and apparent level is estimated at considerable distances. It is now ascertained, that for horizontal refractions the radius of curvature of the curve of refraction is about 7 times the radius of the earth ; in consequence of which, the distance at which an object can be seen by refraction, is, to the distance...
Page 3 - It is true, the surface of the earth is not an exact geometrical globe ; but the inequalities are so inconsiderable, that the highest mountain bears no greater proportion to the bulk of the earth, than a grain of dust does to a common globe. The figure of the earth, then, was reckoned by mathematicians and geographers as perfectly spherical, excepting the small inequalities on its surface, of mountains and vallies ; till an accident engaged the attention of sir Isaac Newton, and M.
Page 6 - ... of a circle is a part of a circle cut off by a straight line drawn across it. This straight line is called the chord. A segment may be either equal to, greater, or less than a semi-circle, which is a segment formed by the diameter of the circle, as CEB, and is equal to half the circle.