Lectures on select subjects in mechanics, hydrostatics, pneumatics, and optics. With the use of the globes, the art of dialing, and the calculation of the mean times of new and full moons and eclipses / By James Ferguson.

James Ferguson

Date:: 1760

Credit: Lectures on select subjects in mechanics, hydrostatics, pneumatics, and optics. With the use of the globes, the art of dialing, and the calculation of the mean times of new and full moons and eclipses / By James Ferguson. Source: Wellcome Collection.

430/486 page 374

$and the axis of the fphere will be equally inclined to both thefe planes. Let WSIE be the equinodtial, whofe elevation above the horizon of Z (London) h 384 degrees *, and PRD be the meridian'of the place Z), cutting the equiriO(5lial in R. Then, it is evident, that the ^yc 'RD is the latitude of the place D, (where the plane Zb would be horizontal) and the are R ^ is the difference of longitude of the planes Zb and DH. In the fpherical triangle WDR^ the arc WD is given, for it is the complement of the plane’s de¬ clination from S the fouth ; which complement is 54° {viz. 90°“—36°) : the angle at jR, in wdiich the meridian of the place D cuts the equator, is a right angle ; and the angle RJVD meafures the elevation of the equino(5lial above the horizon of Z, name]yv38Y degrees. Say therefore, as radius is to the co-fine of the plane’s declination from the fouth, fo is the co-fine of the latitude of Z to the Tne oi RD the latitude of D; which is of a dif¬ ferent denomination from the latitude of Z, be- caufe Z and D are on different fides of the equator. As radius — '— 10.00000 To co-fine 36® o-=:iR^ 9.90796 ^ So CO-fine 51° ^d-=^Z 9.79415 To fine 30'^ i4'=:Z)i? (9.70211) = the lat. of I), whofe horizon is parallel to the vertical plane Zi? at Z. N. B.$