_Magnetic Intensity_ (Vol. vi., p. 578.).--The magnetic intensity is
greatest at the poles; the ratio may roughly be said to be 1.3, but more
accurately 1 to 2.906. This is found by observation of the oscillations of
a vertical or horizontal needle. A needle which made 245 oscillations in
ten minutes at Paris, made only 211 at 7° 1' south lat. in Peru. The
intensity and variations to which it is subject is strictly noted at all
the magnetic observatories, and I believe the disturbances of intensity
which sometimes occur have been found to be simultaneous by a comparison of
observations at different latitudes.
For the fullest information on magnetic intensity, ADSUM is referred to
Sabine's _Report on_ {72} _Magnetic Intensity_, also Sabine's
_Contributions to Terrestrial Magnetism_, 1843, No. V.