se the hail was collected in
a yard surrounded by houses roofed with sheet-iron painted red. The
black colour of the metallic particles enclosed in the hail, their
position in the hail, and finally, the cobalt they contained,
however, indicate in this case too, a quite different origin.

5. In a dust (kryokonite), collected on the inland ice of Greenland
in the month of July, 1870, there were also found mixed with it
grains of metallic iron, containing cobalt. The main mass consisted
of a crystalline, double-refracting silicate, drenched through with
an ill-smelling organic substance. The dust was found in large
quantities at the bottom of innumerable small holes in the surface
of the inland ice. This dust could scarcely be of volcanic origin,
because by its crystalline structure it differs completely from the
glass-dust that is commonly thrown out of volcanoes, and is often
carried by the wind to very remote regions, as also from the dust
which, on the 30th March, 1875, fell at many places in the middle of
Scandinavia, and which was proved to have been thrown out by
volcanoes on Iceland. For, while kryokonite consists of small
angular double-refracting crystal-fragments without any mixture of
particles of glass, the volcanic Haga-dust[191] consists almost
wholly of small microscopic glass bubbles that have no action on the
polarisation-planes of the light that passes through them.

Similar investigations have since been made, among others, by M.
TISSANDIER in Paris, and during NARES' English Polar Expedition.

It may appear to many that it is below the dignity of science to
concern one's self with so trifling an affair as the fall of a small
quantity of dust. But this is by no means the case. For I estimate
the quantity of the dust that was found on the ice north of
Spitzbergen at from 0.1 to 1 milligram per square metre, and
probably the whole fall of dust for the year far exceeded the latter
figure. But a milligram on every square metre of the surface of the
earth amounts for the whole globe to five hundred million kilograms
(say half a million tons)! Such a mass collected year by year during
the geological ages, of a duration probably incomprehensible by us,
forms too important a factor to be neglected, when the fundamental
facts of the geological history of our planet are enumerated. A
continuation of these investigations will perhaps show, that our
globe has increased gradually from a small beginning to the
di