'Dear Sir,

The arrangements we propose to make with you concerning the Instruments of your devising is as follows.

You shall be charged with our ordinary price for the first example made, which shall become your property. After six others have been sold you shall be credited with the amount of the ordinary price of the object, and after every succeeding six have been sold you shall be further credited with the amount of the ordinary selling price of the object at the time. This shall relate to all Instruments which you order to be made form your own drawings & which are bona fide modifications of existing Instruments, or are new Instruments.

This arrangement shall be in force as from January 1st 1881 (except with the case of the Freezing Microtome, which shall start from June 1st 1881) and shall last until December 31st 1881, & shall then be trerminated or renewed by agreement of both parties.

We do not undertake to submit our books for inspection, & our accounts as delivered to you shall be considerd as final.

This agreement shall be considered as strictly private & confidential between you & ourselves.

Faithfully yours

A.G. Dew-smith

Horace Darwin'