. Mathematics, compiled from the best authors and intended to be the text-book of the course of private lectures on these sciences in the University at Cambridge [microform]. at circle, andhave for a stile a small rod parallel to the axis, and hourlines corresponding to those of the great circle ; then thetime, supposed to be shown, would be nearly the sameon both. For a semidiameter of the earth is so small inrespect to the distance of the sun, as not to occasion any ob-servable difference in this case. 4. The time, shown by a dial, is what elapses whilethe suns rays are incident on its face
. Mathematics, compiled from the best authors and intended to be the text-book of the course of private lectures on these sciences in the University at Cambridge [microform]. at circle, andhave for a stile a small rod parallel to the axis, and hourlines corresponding to those of the great circle ; then thetime, supposed to be shown, would be nearly the sameon both. For a semidiameter of the earth is so small inrespect to the distance of the sun, as not to occasion any ob-servable difference in this case. 4. The time, shown by a dial, is what elapses whilethe suns rays are incident on its face ; and the hour lines,8cc. on every dial must be such, as to mark the corres-ponding parts of this time. And the order of the numbersof the hour lines proceeds from the substile in the directionof the motion of the stiles shadow. DIALING. 341 PROBLEMS. PROBLEM I. fo draw a meridian line* Let a time piece be well regulated, so as to show thetime, when the sun is on the meridian. Then at the in-stant, when the sun is on the meridian, let a line be drawnon a plane horizontal surface, in the direction of the shadowof a suspended plumb line ; and it will be a meridian 342 MATHEMATICS. Or, 1. Find an even horizontal surface, or make the sin >othsurface of a board, about a foot square, accurately level j and describe on the surface four or five concentric circlesA, B, C, D, at the distance of about £ inch from one anoth-er, and make the diameter of the outmost nearly a foot. 2. In the centre G fix perpendicularly a pin or rod ofabout •£ inch in diameter, and of such length, that its wholeshadow may fall on the inmost circle four hours or longer :its termination being made round and smooth. 3. Mark the points on the circumference of a circle,where the end of the shadow crosses it both before and afternoon ; as E and F. 4. Bisect the arc, included between the points E, F ;ind the bisecting line GH, drawn from the centre, is a me-ridian line. Note 1. As many meridian lines b
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