8 . SEVENTH REPORT—1837. 
were made during a tour in France, Switzerland, Italy, and 
Germany, with a needle suspended by fibres of silk, vibrating in 
the plane of the horizon, and measuring the horizontal compo- 
nent of the magnetic intensity. The dip was observed at the 
same time with a dipping-needle of Lenoir (the same that had 
been used in the Voyage de Dentrecasteaux), supplying the 
means of computing the total intensity from its horizontal com- 
ponent. An account of these observations was published by 
M. Gay Lussac in the Ist volume of the Memoires de la Société 
d’ Arcueil, The values of the intensity were given in reference 
to the force at Paris, where the needle was vibrated at the close 
of the series, but not at its commencement. M. Gay Lussae 
infers that no change took place in the magnetism of the needle 
throughout the series, from its having had the same time of vi- 
bration at Milan on two occasions, viz. in going and in return- 
ing, at six months’ interval. As no dates are given, the stations 
at which the strict comparability of the force was thereby en- 
sured can only be conjectured. It is probable that no correc- 
tions were applied either for the arcs or for differences of tem- 
perature, as neither of these circumstances is noted in the 
record. The number of stations of known geographical po- 
sition is 19, 16 of which are inserted in the general table in 
this memoir. The other stations were in the crater, on the side, 
and at the foot of Vesuvius, where the results were considered 
by the observers to be affected, as no doubt they were, by the 
proximity of the lava. 
Sabine, 1818, 1819, 1820.—These observations were made 
in the first and second voyages of northern discovery to Baffin’s 
Bay and the Polar Sea. Aware of the magnetic importance of 
the regions to be explored, and anxious duly to improve such 
opportunities, I sought diligently to provide myself with instru- 
ments adequate to the occasion. Those furnished by Govern- 
ment were by no means so; but it fortunately happened that my 
brother-in-law Mr. Browne possessed and entrusted to me a 
dip circle and needle of very superior character, made by Nairne 
and Blunt, and similar in all respects to the one made under 
Mr. Cavendish’s directions, and described by him in the 66th 
vol. of the Phil. Trans. The needle vibrated about eight mi- 
nutes before coming to rest; and probably, from its age, had 
long acquired the state of steady magnetism which it was proved 
to possess during these voyages, its time of vibration being 
almost identical when observed in London in March, 1818, in 
March, 1819, and in December, 1820*. 
* The observations of March, 1819, and December, 1820, are recorded in 
