By M. DUTER.
If we place a thin plate of steel in a uniform magnetic field, so that the
lines of force of the field may be normal to the surface of the plate, we
have a very flat magnet, the two faces of which are the two polar
surfaces. The magnetic distribution thus obtained seems to disappear when
the plate is no longer in the field. The following experiments show that
this disappearance is not complete. I made use of plates of tempered steel
of 1 millimeter in thickness, and varying in diameter from 0.040 to 0.005
meter. With these plates I formed cylindrical batteries. In some of these
batteries the plates are directly in contact, and in others they were
separated by leaves of pasteboard, the thickness of which varied from that
of the thinnest paper to 0.001 meter. The batteries were placed in the
central portion of a very powerful magnetic field, and after they have
been taken out they formed perfectly regular permanent magnets. The
supporting power of these magnets was the greater the nearer its
constituent plates were to each other. In a battery of 100 plates,
touching each other directly, and strongly pressed into a brass cylinder,
the portative force at each extremity rose to 30 grammes. This first
result having been obtained, I dismounted the batteries, plate by plate,
taking care to mark the upper and under side of each. I found then that
each plate retained only an excessively slight magnetism. Yet each of them
still constituted a flat magnet, of which the two faces are the polar
surfaces; for on rebuilding the battery it gave again a perfectly regular
magnet, though weaker than it was at first. The separation of the magnet
into its constituent plates, and its reconstruction, maybe repeated
indefinitely.--_Comptes Rendus._
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Dr. T. Tommasi (_Cosmos les Mondes_) notes that the thermic constant of
thallium is exactly the mean of the thermic constants of potassium and
lead, the two metals which it most resembles in its chemical character.
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