y boundary-line around which a pen attached
to the instrument may be carried'--in the plan of an estate, or a map,
for example, where the plots of ground are often extremely irregular
in form, and difficult to measure, without much complicated
calculation. When Arthur Young wished to ascertain the relative
proportions of cultivated and uncultivated land in France, he cut up a
map of the country, and weighed them one against the other; but the
platometer would have helped him to a more satisfactory conclusion.
The mode by which it effects its purpose is very simple, 'the
essential parts being merely two axles, one of them carrying a cone,
by which the computations are silently performed as the pen proceeds
on its journey; and the other a small wheel, having numbers on it
which tell the result in square measure.' The contents are given with
considerable rapidity, and, it is said, with more exactitude than by
any other process: the instrument, therefore, is practically useful as
well as curious.

Among matters connected with the Academie, Prince Demidoff has asked
for instructions as to how he may best serve the cause of science
during a journey which he proposes to undertake into Siberia,
accompanied by a scientific staff. The prince, who is proprietor of
the richest malachite mines in Russia, has already made similar
explorations in other parts of Europe, and published the results at
his own cost, superbly illustrated, and has presented copies of the
works to most of the scientific societies. He could not have better
advisers for the purpose contemplated, than he will find among those
to whom he has applied. Then a M. Rochas informs the Academie, that a
photographic image on a metal-plate, transferred immediately to
albumenised glass, may be reproduced and multiplied on paper in any
number. Daguerreotypes of waves beating on the sea-shore have been
exhibited, which were taken on glass thus prepared in a very minute
fraction of a second. Add to this, a plan for a double line of
submarine railway from Calais to Dover; a statement from M. Gaietta,
that the aurora borealis is nothing more than spontaneously inflamed
carburet of hydrogen; and a report from a learned anatomist, on the
use, instead of the knife in amputation, of a platinum wire heated
red-hot by a battery--and you may form a notion of the variety of
communications that comes before the French _savans_. M. Peligot
furnishes some details respecting silk-worms. H