[Illustration:  Fig. 3.—­INCANDESCENT GAS LIGHTER.]

Dr. Naret’s Fiat Lux (Fig. 3) is simpler in its operation, and cheaper of application, since it takes its current from the ordinary piles that supply domestic call-bells.  It consists essentially of a fine platinum wire supported by a tilting device in connection with the two poles of a pile composed of three Leclanche elements.  Upon exerting a vertical pressure on the button placed to the left of the apparatus, either directly or by means of a cord, we at the same time turn the cock and cause the platinum spiral to approach, and the latter then becomes incandescent as a consequence of the closing of the circuit of the pile.  After the burner is lighted it is only necessary to leave the apparatus to itself.  The cock remains open, the spiral recedes from the burner, the circuit opens anew, and the burner remains lighted until the gas is turned off.  This device, then, is particularly appropriate in all cases where there is a pressing need of light, for a single maneuver suffices to open the cock and effect a lighting of the burner.—­La Nature.

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DISTRIBUTION OF HEAT WHICH IS DEVELOPED BY FORGING.

On the 8th of June. 1874, Tresca presented to the French Academy some considerations respecting the distribution of heat in forging a bar of platinum, and stated the principal reasons which rendered that metal especially suitable for the purpose.  He subsequently experimented, in a similar way, with other metals, and finally adopted Senarmont’s method for the study of conductibility.  A steel or copper bar was carefully polished on its lateral faces, and the polished portion covered with a thin coat of wax.  The bar thus prepared was placed under a ram, of known weight, P, which was raised to a height, H, where it was automatically released so as to expend upon the bar the whole quantity of work T=PH, between the two equal faces of the ram and the anvil.  A single shock sufficed to melt the wax upon a certain zone and thus to limit, with great sharpness, the part of the lateral faces which had been raised during the shock to the temperature of melting wax.  Generally the zone of fusion imitates the area comprised between the two branches of an equilateral hyperbola, but the fall can be so graduated as to restrict this zone, which then takes other forms, somewhat different, but always symmetrical.  If A is the area of this zone, b the breadth of the bar, d the density of the metal, c its capacity for heat, and t-t0 the excess of the melting temperature of wax over the surrounding temperature, it is evident that, if we consider A as the base of a horizontal prism which is raised to the temperature t, the calorific effect may be expressed by: 

  Ab x d x C(t-t0);

and on multiplying this quantity of heat by 425 we find, for the value of its equivalent in work,