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

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T. and J. Hodgson and sold by E. Charnley, 1838 - 106 pagina's
 

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Pagina 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.
Pagina 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.
Pagina 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.
Pagina 35 - ... ruler wherein it is fixed is level. When it is not level, the bubble will rife to one end. Thi...
Pagina 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...
Pagina 22 - ... in sea miles and parts ; under the former, and opposite the latter, stands the dip of the horizon, which is to be subtracted from the altitude observed by a fore observation jnstcad of the numbers in Table XIII.
Pagina 27 - The whole is mounted on parallel plates and three legs, the same as the theodolite. It is evident, from the nature of this instrument, that three adjustments are necessary. First, to place the intersection of the wires in the telescope, so that it shall coincide with the axis of the cylindrical rings on which the telescope turns ; secondly, to render the level parallel to this axis ; and lastly, to set the telescope perpendicular to the vertical axis, that the level may preserve its position while...
Pagina 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.
Pagina 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.
Pagina 20 - ... telescope to be in a right line ; this was done in the afternoon. The following morning proved uncommonly dewy, and the sun shone bright ; when, having occasion to replace the telescope...

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