My dear Owen

I do not know whether your MS. instructions are sent in; but even if they
are not sent in, I daresay what I am going to write will be absolutely
superfluous (25/1. The results of Mr. Darwin's experience given in the
above letter were embodied by Prof. Owen in the section "On the Use of the
Microscope on Board Ship," forming part of the article "Zoology" in the
"Manual of Scientific Enquiry, Prepared for the Use of Her Majesty's Navy"
(London, 1849).), but I have derived such infinitely great advantage from
my new simple microscope, in comparison with the one which I used on board
the "Beagle," and which was recommended to me by R. Brown ("Life and
Letters," I., page 145.), 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 and fixed. Mine will hold a saucer
three inches in inside diameter. I have never seen such a microscope as
mine, though Chevalier's (from whose plan many points of mine are taken),
of Paris, approaches it pretty closely. 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.
But pray again believe that I feel the absurdity of this letter, and I
write merely from the chance of yourself, possessing great skill and having
worked with good instruments, [not being] possibly 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