Address:
Cap^t Mathew [sic] Flinders R.N.
    Mary Street
      Fitzroy Square

Annotation:
Nov. 10.1812 M^r Horsburgh

                East India House
                    10^th Nov^r 1812

Sir
    The Editor of the Naval Chronicle has communicated
to me, some Observations made by you, on an extract from
the Introduction of my Directions for Sailing to & from India &c.
which appeared in the N.C. of last month. — The observations
you have made relative to the denomination of the magnetic
from the true meridian, are perfectly correct — I was led into
the error you have noticed by the perusal of some Book which
I had taken a note from, and being busied correcting the {Proofs}
and making an Index to my Book, at the time I was writing
the Introduction, I did not consider the subject in my mind
when I adverted to the Variation, but after the Book was
published I perceived my mistake when it was too late
to correct it. — Had I apprehended the Editor of the Naval
Chronicle intended to have extracted any thing from the
Introduction of the Book, I should certainly have apprised him
of my mistake, which I hope will be of no material consequence,
as few Sailors I fancy will take the trouble to peruse the
Introduction.

    Your paper on the Variation published in the Philosophical
Transactions, much attracted my attention, and having been at
the meeting of the Royal Society when it was read, I was
induced to ask my friend Cap^t Heywood to make some obs^ns
at Spithead, conceiving that to be a convenient place where the

ships ride with their heads well to the East & Westward on the
different tides, — and as I thought the phenomena interesting and little
known to any except yourself, some observations made in a high
Northern latitude might be of utility to compare with yours made in the
Southern hemisphere. — My friend Heywood after taking several obs^ns on
each tide, said he could perceive little or no difference but what seemed
to arise from the small change of the ships position in swinging to the
different tides.

    Heywood sent me a copy of the results of your last observations taken
at Spithead, but these could not be noticed in my Directions, which were
published in Aug^t . 1811, otherwise I certainly should have noticed them; —
for I assure you Sir, like yourself, I trust my endeavours are directed
entirely to approximate to truth, and contribute if poƒsible, to assist
in clearing the way for my Brother sailors.—
    I regret that I had not the honor to be personally acquainted with
you before this time; some time ago I was about to have called on you,
being informed you lived in Naƒsau Street, but afterward I learned you
had moved. —

    Should you paƒs the India House at any time, I shall be happy
to see you, where I am daily to be found in the Map-room until
2 P.M.
      With respect & esteem
          I am Sir
              Your Obd^t & most hble Servt
                Jas. Horsburgh