mirrors is fixed, and gives a line of reference; the other is attached
to the magnetic bar, whose slightest movements it reproduces upon the
sensitized paper. The moments when direct observations were taken were
carefully recorded. The magnetic _pavilion_ was made of wood and copper,
placed at about fifty-three feet from the dwellings or camp, near the
sea, against a wooded hill which shaded it completely; the interior
was covered with felt upon all its sides, in order to avoid as much as
possible the varying temperatures.

The diurnal amplitude of the declination increased uniformly from the
time of their arrival in September up to December, when it obtained
its maximum of 7'40", then diminished to June, when it is no more than
2'20"; from this it increased up to the day of departure. The maximum
declination takes place toward 1 P.M., the minimum at 8:50 A.M. The
night maxima and minima are not clearly shown except in the southern
winter.

The mean diurnal curve brings into prominence the constant diminution
of the declination and the much greater importance of the perturbations
during the summer months. These means, combined with the 300 absolute
determinations, give 4' as the annual change of the declination.

M. Mascart's apparatus proved to be wonderfully useful in recording the
rapid and slight perturbations of the magnet. Comparisons between the
magnetic and atmospheric perturbations gave no result. There was,
however, little stormy weather and no auroral displays. This latter
phenomenon, according to the English missionaries, is rarely observed in
Tierra del Fuego.

The electrometer used at the Cape was founded upon the principle