Page:The story of the comets.djvu/226

172 their calculations do not always give the perihelion distance of a comet or its periodic time of revolution round the Sun; but limit themselves to announcing the angle of the eccentricity, the mean daily motion , and the logarithm of the semi-axis major or mean distance (a); leaving the student to find out for himself the perihelion distance (q) and the period.

(i.) Look out in a Book of Tables the Natural Sine of 24° 20' 26". (ii.) Subtract this from Unity (1⋅0). (iii.) Find the logarithm of the result. (iv.) Add this to the logarithm of a. (v.) And this will give the logarithm of q.

(i.) Calculate number of seconds of arc in 360°. (ii.) Find logarithm of that number of seconds.