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The Flinders papersletters and documents about the explorer Matthew Flinders (1774-1814)
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Loose pages from Flinders' private letterbook (6 of 6). Letters to Charles Desbassayns on financial matters and magnetic research. (FLI04)

Cover sheet:
Letter on
Magnetic Researches,
Capt Matthew Flinders
M. Charles Desbassayns
12 June 1808

    Cut from Private Letter Book, to be
    Restored to it when done with


hes had taken had produced any benefit, at the same time I wrote you to inform
you of these circumstances, and requesting to be acquainted with requesting to be informed of the state of the af-
fair, offered to write to Mr A. Baudin should you not have found means
to convey the information to Mr H; for when the question was to obtain means
for a servant to enter the prison, I thought it too trivial, but now that the
liberty of my countryman appeared to depend upon ^ his interference, the case was become dif-
ferent; and I repeat, that the it was never the idea of compromising Mr
A Baudin with the government that prevented me from writing to him, but
the small importance of the affair compared to ^ the person to be employed, and the little intimacy I have
with him: the first is too refined for the comprehension of an Englishman.
      After the This, my friend, is the state of the matter, as I have consider-
ed it. The man who has been honoured with your friendship, ought not to
^ pass over in silence the charge that he sought to engage the friends of another in an affair which he found too dangerous to risk his own, and I leave it to your candour
to say whether I have merited it.
      No, my friend, I have had seen too many proofs of the goodness of your
heart, and have received too many myself, to believe you can be indifferent
to the lot of an honest man; but you will acknowledge, that according to
my ideas as expressed of the subject as expressed above, with which I was
born and with which perhaps I shall die, and knowing, as I do, the active
benevolence of your disposition, that it was a matter of surprise to me
that you should find have so much difficulty in finding amongst your numerous
acquaintances, some one who would perform the little offices for which we had
occasion; and according to my manner of thinking, I could only attribute it to the
fears of Mr Pitot ^ under the existing circumstances, which seem to be pushed to the extreme I could not comprehend with whose wishes I know you almost made it a passion
to conform. Had I considered the matter as you do, I should have had
no surprise, but neither perhaps should I have ^ dared to write written to Mr de Kerjean
for now I see, that this step on my part must appear to him equally incon-
siderate as if some one was to address himself ^ at this time to Mr Pitot for a simi-
lar service, one being no for the one is no better more in the good graces of the government than
the other, or possessing more friends. Think not, my friend, that I am indifferent
to your position, on the contrary, it has given me much pain that you should
have adopted the step of writing to Mr Humphreys yourself, since you, who know
much better than me the light in which the government may consider it, think
it may produce disagreeable consequences. I know that heretofore you had en-
gaged Thomy Laverge to visit a prisoner in the position of Mr Humphreys, and
I could

I could not foresee that some similar step should be now impossible. Ardent
minds are subject to moments of ebullition, and ^ it was probably in one of these I judge it was in such a sent-
ment that you ^ adopted such a measure took such steps, and penned the letter which I received yes-
      I will not longer dwell upon this unpleasant subject, but requesting you
to enlighten my mind where you see that I am wrong, conclude with my best wishes
for your speedy deliverance from the embarrassing circumstances in which your
house unfortunately finds itself with this extraordinary government.
        your most affectionate and sincere friend
            Mattw Flinders

Mr Charles Desbassayns – Riviàre des pluise, pràs de St Denis – Bourbon
                        Tamarinds June 12 1808
My dear Charles
dated             It was with the greatest pleasure I received your letter
of the 5th and 11 of May, on the 23 following. Every article in it, your
abominable cold excepted, was a new subject of satisfaction. I find
you have obtained an interest beyond what I expected for the sum
^ of which you have the had the goodness to take the management for me; but I
acknowledge, that this circumstance does not give me so much pleasure as
the good security upon which the principal is placed. I beg of you afresh, to
set for me as you would for yourself, and consequently you will not require
for me what you are not in the habit if doing for what yourself, or what the
customs of the island do not allow. With respect to the expenses of manage-
ment, it is most prudent for me to leave that also to your sole discretion,

^ with the request that you will be just towards yourself; and I shall leave directions to allow all such as you, or any one for you,
may shew authority for, in deduction of the interest that may have arisen.
      I think my dear Charles there is now no longer any necessity for our
letters to be filled with this subject; I would occupy as little of your time
valuable time as possible, and little I would have devoted to friend-
ship, and to subjects of literature which interest us both. Make ^ it not there-
fore any point of obligation to write to me regularly, or to answer every letter
that you may receive; my pride on one hand, and my confidence in your
friendship on the other, will prevent me from thinking you can neglect me;
and besides, I am not naturally of that unquiet class that think a few days de-
lay ^ or weeks, delay according to circumstances in answering an ordinary letter to be an unpardonable fault. I know
Since the correspondence between our good Madame D'Ari-
and her daughter has become regular, ^ I have known how unceasingly you are occupied,
but at

but at the epoch in which I begged you to take the management if the little
affair I wish to leave in this country, I had not an idea of their multiplici-
ty, otherwise I should not have had the courage, or the imprudence which
you will, to have added to the burden; at all events do not let the trouble
of writing ^ often to me often increase it, but put yourself wholly at your ease there-
on. I took, who ought naturally to be the most idle person in the Isle of France
have my occupations, which sometimes keep me even till one and two o'clock in
the morning when the fit takes me, for in that, as in some other particulars there
is much sympathy of disposition between us, when once an idea has got posses-
sion of me, I pursue it with an ardour which does not cease until success or
defeat naturally produces a termination. Three or four months since ^ the geography of Madagas-
car was the subject of my enquiries, and continued until I had exhausted
all the information I could procure, and had placed arranged it upon a
chart, to that was added and made out an accompanying memoir. To
that succeeded a renovation of the subjects of the changes in the declina-
tion of the compass which take place on ship board on altering changing the direc-
tion of the ship's head; and this led me to ^ make researches into upon the situation of
the two great attractive points within the earth which affect the dipping
needle, and of the two corresponding points upon the surface which go-
vern the needle to which the needle of the mariners compass is directed;
these have closely occupied me ever since, and it is only this morning that I
have laid aside the my memoir the rough manuscript containing my
unarranged ideas upon these subjects. It will remain with Madagascar
and some other matters until I find time and tranquillity to put them
in order, and can obtain all the requisite observations to bring ^ advance them to perfec-
tion. Upon the magnetic effect of ships first of these subjects I am as much satisfied with the re-
sults as the present state of my authorities can well permit. I am pretty
well able to assign the cause —
1st Why such changes in the variation take place on altering the
ship's head
2 Why they assure a contrary nature in the southern and in the northern
magnetic hemispheres
3 Why the changes diminish on approaching the magnetic equator and disap-
pear upon it. To these, my enqu late enquiries have added, the
4 The law which govern these changes whilst in the same place, and I am

satisfied is no other than that the changes are proportional to the {rises} of
the angles of deviation which the ship's head makes with the magnetic mer-
idian; and
5th The law by which these changes are governed in different parts of the
earth, and which is, that they are directly proportionate to the dip of the
needle at those parts ^ on board a ship when her head deviates from the meridian;     thus if the change is 2° ^ at a place where the dip is 35° it will
be 4° in the same case where the dip ^ where it is 70°; provided the quantity and disproportion of
the magnetic [illegible] on the ship board remains the same.
        Thus far, I believe, my subject is untouched by any other ^ person; but in order
to prove my facts and conclusions to the satisfaction of others, I require
a regular series of observations made with this point in view, on board more than
one vessels at two or three stations widely distant.
        With respect to the magnetism situation of the magnetic poles, you will
conclude that I have much impatience to see the manuscript of M M.
Humboldt and Bist, especially as from what you say I suspect our conclusi-
ons will ^ nearly be the same. The points upon the surface to which the needle seems to be
most generally directed are in 74°40' N and 88°40' W in one hemisphere, and in
73°30' south and 134° east ^ of Greenwich in the other; but it appears, that America, particularly near
Cape Horn, and Madagascar, have a great effect upon the needle; the for-
mer so much so as to render it difficult to point out assign the situations of the ^ great at-
tractive points; I had besides another difficulty, and all others to this time must
have nearly had the same, which is the being obliged to make my deduc-
tions from observations which ^ my own excepted have not received the necessary corrections;
my conclusions thereon are therefor deferred until I ^ can make a collection
of observations in different parts of the earth, with the necessary data to
divest them of the error arising from the ship.
      Considering that the two magnetic poles of the earth must be equal in force,
and produce 90° of inclination at the point immediately above one as above
the other, I conclude that the difference between the squares of their distan-
ces must be the same at each, and ^ that these squares must be as 1 is to 2, the roots of which are 1 and
1,414214; or in parts of the semidiameter of the earth, the distances of the
poles from the points above on the surface are 0,828427 and 1,171573
the squares of which are equally the double the one of the other; they should
therefore be no more than 0,171573 of the semidiameter distant from the
center of the earth; and from what you say, I judge this is nearly M.M.
H and B's determination. These positions ^ taken exactly on opposite sides of the center give me 70 ¼ of inclination at
Paris where M. {Haüy} says it is 72° and 66° on the south coast of Aus-
tralia where I observed the same; but with four other observations nearer
the equa-

equator it differs from 2° to 9°; taking the poles at the same distances from the
center but under the points on the surface deduced from the imperfect va-
reations ^ above mentioned, two of the is my six observations come exact, two differ 3° and the
other two 6° so that I am not satisfied as to the exact position.
      Mr {Haüy}concludes that the magnetic power sum of the magnetic
attractions and repulsions ^ are every where the same but I judge with M.M. H and B that it
augments from the ^ magnetic equator to the poles, in ^ about the proportion 2002 to 2032
but it is the difference of power between the one pole and the other that
most interests me, [illegible] since it varies with
each change of place, the dip and causes inclination being produced by the of the needle, and the changes of va-
^ riation on ship board. I have tried exercised my little knowledge to arrive at this directly,
by means of the inclination alone, and thence to deduce the place
of the poles from the observations, but have been obliged to assume
give that up, and assume places for the poles to try whether the incli-
nation obtained therefrom agreed with the observations; and since the
calculations are rather long, the time and trouble ^ a number of these essays have
given me, are considerable.
      The position of the poles so near the center of the earth is certain-
ly very different to that of the poles of an artificial magnet, but
I do not conceive it necessary to conclude from thence that there is
a magnet lodged in the center. The earth is a heterogeneous mass
containing many isolated magnetic substances, each of which has
its particular poles; these poles form amongst them a common
center for each species of attraction, and which, as in gravity, will
be at the center of all the masses combined; so that could we annihi- change
late half the magnetic substances in one hemisphere into non-mag-
netic, the ^ mean points of magnetic attractions poles, according to my idea, would retreat into the both
center in the other hemisphere. I have remarked an effect on ship board which illustrate
this: a ship as containing various isolated magnetic substances, is
^ in this respect analogous to the earth. My observations shew the attraction of effects
of the attractive point in the ^ Investigator ship to have ^ been greater in the northern
hemisphere than in the south at the same dip; but during the passage I removed two guns
^ and some other iron from the after part of the ship forward, by which ^ it appears I judge the com-
mon centers of the attractions on board was removed further from the
binnacle, and the power ^ of the upper point on the compass, confined to that of the poles
upon it became thereby lessened in the proportion, as the observations

shew of 62 to 54 according to the observations.
      I attach myself most to what concerns the magnetism of ships,
as being that which I understand best, and which promised to be of con-
siderable practical utility to seamen, and to those employed in marine
surveying particularly; neither should do I think it improbable that
with the aid ^ of the corrections the almost forgotten variation chart may be revived with
advantage. These, ^ my voyage and some other subjects relating to my profession
will furnish me with food for employment and food for speculation in the retirement to which
I may probably be condemned on my return to England. They have
already been of much service to me, was it only to have driven off
the mortal inquietude into which my long and extraordinary imprison-
ment might otherwise have plunged me.     Apropos de cela, je n'ai rien de
nouveau depuis long temps, pas un mot ne passe entre Son Excellence
et moi ^ depuis Octobre dernier et je n'attends rien, si ce n'est une lettre de L'Inde
par le cartel quand il arriviere. La Semillante est disarmé, et
ne sorte plus, dit-on. On pretend que le général attend incessamment au frigate
de France portant résponse à ses depêches par l'Apropos, et c'est
possible qu'un renouvellement de l'ordre pour me mettre en liberté et
remettre mon petit batiment peut [illegible], mais il restirait à savoir
si l'execution s'en suiverait.
      Adieu, mon cher Charles; envoyez moi le manuscript quand
vous pouvez le trouver. Presentez mes amities les plus respectueuses
et sincere à votre chere et bonne femme, et croyez moi être, avec
la plus parfaite amitie.
      Votre tràs obligà, tràs affectionné, et tràs humble
      serviteur     Mattw Flinders

Rough translation of the above:
    Apropos of that, I haven't had anything new in a long time, not a word has passed between His Excellency and myself since last October, and I have not had a letter from India. La Semillante is disarmed and no longer leaving – so they say. They claim that the general waits shortly for a frigate from France carrying a response to his despatches and it is possible that a fresh order to put me at liberty and to give me my small boat back might come, but it remains to see if the execution of it will follow.
    Adieu my dear Charles, send me the manuscript when you have found it. Give my very best and respectful and sincere wishes to your dear and beautiful wife, and believe me to be with the most perfect friendship
      your very obliged, very affectionate and very humble
      servant     Matthew Flinders

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Flinders, Matthew
Desbassayns, Charles
Pitot, Thomas

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Ile de France (Mauritius)

La Semillante

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