From John Murray   7 May 1861

My Dear Sir

I enclose my amended note of hand for £372 for the 3^rd edition of your work on Species¹

This, as far as I can judge, is the amount of $\frac{2}{3}$ ^d profit arising from 2000 copies.² There are always contingencies arising—such as advertising expences, which make it difficult to fix beforehand the precise profits on any work.³ Thus in the first Edition—the sum I gave you turned out far more than $\frac{2}{3}$ ^d or at least my share eventually fell below $\frac{1}{3}$ considerably.⁴

Moreover it must be borne in mind that it is not a mere rule of 3 sum to calculate profits of a book— Thus—the 3^rd. Edⁿ. of 2000 Copies cost only £70. less than 3000 of the 3^rd. edition. Moreover this last is increased by two sheets beyond the second edition 23 shts instead of 21.

I enter into these details to prevent any misunderstanding and hope I have been successful.

If we print any more editions I would prefer deferring the settlement untill the whole is disposed of when I could arrange the amount of $\frac{2}{3}$ds. profit to the uttermost farthing.⁵

I remain | Dear Sir | Y^rs. Very faithfully | (signed) John Murray

C. Darwin Esq