3. The magnetisation of my impure nickel disappears about 310° C.

4. A little below the temperature of 310° C. the induction diminishes very rapidly with increase of temperature.

5. At lower temperatures still the induction increases with rise of temperature for low forces, diminishes for high forces. This fact has been observed by several experimenters.

Specific Heat. The object here was simply to ascertain whether or not there was marked change at the temperature when the nickel ceases to be magnetic. It appeared that this question could be best answered by the method of cooling, and that it mattered little even if it were roughly applied. A cylinder of nickel (fig. 2, Plate 13) was taken, 5·08 cm. diameter, 5·08 cm. high, having a circumferential groove, 15.9 mm. deep and 635 mm. wide. In this groove was wound a copper wire, well insulated with asbestos, by the resistance of which the temperature was determined. The cylinder was next enveloped in many folds of asbestos paper to insure that the cooling should be slow, and that consequently the temperature of the nickel should be fairly uniform and equal to that of the copper wire. The whole was now heated over a bunsen lamp till the temperature was considerably above 310° C.; the lamp was next removed, and the times noted at which the resistance of the copper wire was balanced by successive values in the Wheatstone's bridge. If @ be the temperature, and t be time, and if the specific heat be assumed constant, and the rate of do loss of heat proportional to the excess of temperature, k dt

+0=0

or k log + (t−to) = 0. In curve 21 the abscissæ represent the time in minutes, the ordinates the logarithms of the temperature; the points would lie in a straight line if the specific heat were constant. It will be observed that the curvature of the curve is small and regular, indicating that although the specific heat is not quite constant, or the rate of loss is not quite proportional to the excess of temperature, there is no sudden change at or about 310° C. Hence we may infer absorption or libera

that in this sample there is no great or sudden

tion of heat occurring with the accession of the property of magnetisability.

VIII. "Experiments on Carbon at high Temperatures and under great Pressures, and in contact with other Substances." By the Hon. CHARLES A. PARSONS. Communicated by the Right Hon. the EARL OF ROSSE, F.R.S. Received June 13, 1888.

The primary object of these experiments was to obtain a dense form of carbon which should be more durable than the ordinary carbon when used in arc lamps, and at the same time to obtain a material better suited for the formation of the burners of incandescent lamps.

There were a considerable number of experiments made in which the conditions were somewhat alike, and many were almost repetitions with slightly varying pressures and temperatures. They may, however be divided into two distinct classes: the first in which a carbon rod surrounded by a fluid under great pressure is electrically heated by passing a large current through it, the second in which the liquid is replaced by various substances such as alumina, silica, lime, &c.

The arrangement of the experiment was as follows:-A massive cylindrical steel mould of about 3 inches internal diameter and 6 inches high was placed under a hydraulic press; the bottom of the mould was closed by a spigot and asbestos-rubber packing similar to the gas-check in guns; the top was closed by a plunger similarly packed; this packing was perfectly tight at all pressures. In the spigot was a centrally bored hole into which the bottom end of the carbon rod to be treated fitted, the top end of the carbon rod was connected electrically to the mould by a copper cap which also helped to support the carbon rod in a central position. The bottom block and spigot were insulated electrically from the mould by asbestos, and the leading wires from the dynamo being connected to the block and mould respectively, the current passed along the carbon rod in the interior of the mould.

The fluid was run in so as to cover the rod completely. The plunger was then free to exert its pressure on the liquid without injuring the carbon. The pressure in the mould was indicated by the gauge on the press.

Experiments. Class I.

Among the liquids tested were benzene, paraffin, treacle, chloride and bisulphide of carbon.

The pressures in the mould during the several experiments were maintained at from 5 to 15 tons per square inch; the initial size of the rod was in all cases 4-inch, and the current from 100 to 300 ampères.