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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IMPROVED GAS LIGHT BUOY.

[Illustration:  GAS LIGHT BUOY.]

The accompanying engravings represent a light buoy made by the Pintsch’s Patent Lighting Company for the river Humber.  The chief dimensions of the buoy are given in the engraving, which also shows that the gas holder is placed within the boat in such a way as to be protected from blows likely to cause any leakage.  The buoy has a special form to meet its requirements as a lightship, and the conditions of its employment is the fast tidal current of the river.  It was designed by Mr. C. Berthon, of Westminster, and is intended to carry a six months’ supply of gas, the burner, regulator, and lamp being on the well known Pintsch system.  The hull is formed of 3/8 inch plate, 24 feet 3 inches total length, and 9 feet beam at the line of flotation.  The laps