CHAP II.
Shewing the making of a direct Verticall Diall for an Oblique Sphear, that is, a direct North or South Diall plane.
EVery plane hath a Verticall point, and for the making of a Verticall Diall for the Latitude of London, out of the theoricall demonstrati∣on Chap. 7. Praecog. Astron▪ take the semidia∣meter of the Verticall, and with that, as with the semidiameter of the Horizon, describe a Quadrant, & draw the tangent line FG, and with the semidiameter of the Aequator finish all as in the Horizontall: the Style must proceed from the center A, and be elevated from the Meridian line AF, so much as is the complement of the E∣levation of the Pole, and must point toward the invisible Pole, viz. the South Pole, and hath but 12 houres on it.
The Arithmeticall Calculation.
As the Radius,
Is to the tangent of the Aequinoctiall distance of the houre from the Meridian;
So is the Co-sine, that is, the complement sine of the elevation, to the tangent of the houre distance from the Me∣ridian required.
