Celejlial and terrestrial Globes. 333

the sun should be depressed 12 degrees be-low the horizon, that the star may appearfree from the solar rays: having noted thepoint a, on the ecliptic, move the quadrantuntil the 12th degree below the horizonintersects the ecliptic at s, then Z s will re-present a vertical circle, in which the sunat s is depressed 12 degrees.

So in the triangle a C S, right angled atC, we have the sides C S, 12 degrees, therequisite depression of the fun below thehorizon, to free the star from his rays, orthat point of the ecliptic at 8, to make thestar at A- first heliacally visible when it rises,or from which we may fee upon the etherside of the globe when it sets heliacally.

The angle S a C is the altitude of thenonagesimal, or inclination of the planes ofthe' ecliptic and horizon; and the angle atC right, being formed by the intersectionof a vertical circle with the horizon: themeasure of the angle S a C, is obtained byinspection on the brass meridian from Oto vs, the point in which the tropic of Ca-pricorn cuts that circle; the side a S, beingan arch of the ecliptic, through which thefun passes, from the time the star at v rises

with