Page:The story of the comets.djvu/227

XI. (iii.) Find logarithm of number of seconds travelled over by comet in 1 day. (iv.) Divide the number of seconds in 360 by number of seconds travelled over by comet in 1 day by subtracting the logarithm of the latter from the logarithm of the former. (v.) Quotient will be comet's period in days.

(i a.) 1296000". (ii a.) Logarithm of this number = 6⋅1126050. (iii a.) Mean daily motion being 517"⋅44, logarithm of mean daily motion = 2⋅7138600. (iv a.) Subtract one of these logarithms from the other—

∴ Period = 2504⋅7 days. = 6⋅8 years.