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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 —
1^st 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