. 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]. equinoctial for our latitude. problem v. To draxv geometrically a polar dial, or a horizontal dial at the equator. 1. Draw two parallel lines AB, DE, at a convenient dis-tance for inscribing the hour lines. 2. Draw MCF, mcf, perpendicularly from AB acrossDE, making CF, cf, each equal to the height of the stile,and Cc equal to its thickness, for the XII oclock line. 3. On the centres F, f, and with any convenient radius,as
. 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]. equinoctial for our latitude. problem v. To draxv geometrically a polar dial, or a horizontal dial at the equator. 1. Draw two parallel lines AB, DE, at a convenient dis-tance for inscribing the hour lines. 2. Draw MCF, mcf, perpendicularly from AB acrossDE, making CF, cf, each equal to the height of the stile,and Cc equal to its thickness, for the XII oclock line. 3. On the centres F, f, and with any convenient radius,as FC, describe the quadrants CH, cG. Divide eachquadrant into 6 equal parts, at m, m ; n, n, &c. and drawlines from the respective centres F, f, through all the points • of division till they intersect the line DE in the points I, II,&c. numbered toward the east from the XII oclock through the points I, II, he. draw lines from DE toAB parallel to MC ; and they will be the hour lines. 3\S MATHEMATICS. FIGURE 1. K v m 5E2 HI I JTx: i x j • i poll ill IEEE i i7v r I ,-;.r:—ra:_ tc— n \ —i—;-—r x^lfclx x-^v: J? s. v \ >* ••--. \v. 5?. *x v o £ J? H Note 1. The stile of this dial may be a plate in form of aparallelogram, of the thickness Cc, length MC, and heightMK = CF ; and it must be set on MCcm, perpendicular tothe plane of the dial; and the shadow of the top points tothe time. Note 2. When this dial is used, its plane must be setparallel to that meridian, which is perpendicular to the me-ridian of the place ; that is, with the XII oclock line par-allel to the axis of the earth, and a line perpendicular to it,as AB, horizontal. Note 3. If the stile be considered as a mere geomet-rical plane, the line MC may be taken for its base, and asemicircle must be described on F, and divided into 12parts ; and the rest of the process will be the same as before*A similar observation is applicable to odier dials. DIALING. 349 FIGURE 2. ?E •I if iff K IF3 m i
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