The idea of employing a magnet as compensator in a magnetic balance is
not new, this disposition having been used by Prof. Von Feilitzsch in
1856 in his researches on the magnetizing influence of the current. In
Von Feilitzsch's balance, however, the compensating magnet was placed
end on to the needle, and its directive action was diminished at will,
not by turning it round on its center, but by shifting it to a greater
distance along a linear scale below it. The form now given by Hughes to
the balance is one of so great compactness and convenience that it
will probably prove a most acceptable addition to the resources of the
physical laboratory.--_Nature_.
* * * * *
HOW TO HARDEN CAST IRON.
Cast iron may be hardened as follows: Heat the iron to a cherry red,
then sprinkle on it cyanide of potassium and heat to a little above red,
then dip. The end of a rod that had been treated in this way could not
be cut with a file. Upon breaking off a piece about one-half an inch
long, it was found that the hardening had penetrated to the interior,
upon which the file made no more impression than upon the surface.
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