to add, (because I am sure you will believe it sincere,)
with the highest admiration. Go on thus, and you will leave a
memorial of no common kind to posterity; and, what you will value
far more than fame, you will have accomplished a most useful work.
What a pity that La Place has not lived to see this illustration of
his great work! You will only, I fear, give too strong a stimulus to
the study of abstract science by this performance.

I have marked as somewhat obscure a part of the illustration of the
principle of virtual velocities.... Will you look at this point
again? I have made a trifling remark in page 6, but it is a mere
matter of metaphysical nicety, and perhaps hardly worth pencilling
your beautiful manuscript for.

Ever yours most truly,
J. HERSCHEL.

[In publishing the following letter, I do not consider that I am
infringing on the rule I have followed in obedience to my mother's
wishes, that is, to abstain from giving publicity to all letters
which are of a private and confidential character. This one entirely
concerns her scientific writings, and is interesting as showing the
confidence which existed between Sir John Herschel and
herself. This great philosopher was my mother's truest and best
friend, one whose opinion she valued above all others, whose genius
and consummate talents she admired, and whose beautiful character
she loved with an intensity which is better shown by some extracts
from her letters to be given presently than by anything I can say.
This deep regard on her part he returned with the most chivalrous
respect and admiration. In any doubt or difficulty it was his advice
she sought, his criticism she submitted to; both were always frankly
given without the slightest fear of giving offence, for Sir John
Herschel well knew the spirit with which any remarks of his would be
received.]

FROM SIR JOHN HERSCHEL TO MRS. SOMERVILLE.

SLOUGH, _Feb. 23rd, 1830_.

MY DEAR MRS. SOMERVILLE,

... As you contemplate separate publication, and as the attention of
many will be turned to a work from _your_ pen who will just possess
quantum enough of mathematical knowledge to be able to read the
first chapter without being able to follow you into its application,
and a