My dear Owen

I do not know whether your M.S. instructions¹ are sent in; but even if they are not sent in, I daresay what I am going to write will be absolutely superfluous, but I have derived such infinitely great advantage from my new simple microscope,² in comparison with the one, which I used on board the Beagle & which was recommended to me by R. Brown,³ that I cannot forego the mere chance of advantage of urging this on you. The leading point of difference consists simply in having the stage, for saucers very large & fixed. mine will hold a saucer 3 inches in inside diameter I have never seen such a microscope, as mine, though Chevaliers (from whose plan, many points of mine are taken) of Paris approaches it pretty closely.—⁴ I fully appreciate the utter absurdity of my giving you advice about means of dissecting; but I have appreciated myself the enormous disadvantage of having worked with a bad instrument, though thought a few years since the best. Please to observe that without you call especial attention to this point; those ignorant of natural History, will be sure to get one of the fiddling instruments sold in shops. If you thought fit I would point out the differences, which from my experience, make a useful microscope for the kind of dissection of the invertebrates which a person would be likely to attempt on board a vessel.⁵ But pray again believe that I feel the absurdity of this letter & I write merely from the chance of yourself possessing great skill & having worked with good instruments, may not possibly be fully aware, what an astonishing difference the kind of microscope makes for those who have not been trained in skill for dissection under water.

When next I come to town (I was prevented last time by illness), I must call on you, & report for my own satisfaction, a really, (I think) curious point I have made out in my beloved Barnacles:⁶ you cannot tell how much I enjoyed my talk with you here.

Ever, my dear Owen | Yours sincerely | C. Darwin

P.S. If I do not hear, I shall understand that my letter is superfluous.— Smith & Beck were so pleased with the simple microscope they made for me; that they have made another as a model: if you are consulted by any young Naturalist, do recommend them to look at this; I really feel quite a personal gratitude to this form of microscope & quite a hatred to my old one.—