Progress of Invention. 473 



PROGRESS OF INVENTION. 



Improvement of Davy's Lamp. — Many improvements of this 

 most valuable apparatus have been invented : one, very recently 

 proposed, consists in the application of an outer cylindrical case, 

 which is made, in part, of glass, and in part, of "wire gauze. Both, 

 cases have independent fastenings, and therefore are not likely to 

 be opened by any accident, nor, in ordinary circumstances, can they 

 be opened even by design. Experiments made with this lamp have 

 shown that it is much more to be relied upon than the ordinary 

 kind : since it remains perfectly cool, in an atmosphere in which an 

 ordinary Davy's lamp would be very soon heated to redness. 



Steam Boiler Incrustations. — These, a prolific source of 

 steam-boiler explosions, consists of earthy substances, that are 

 bad conductors of heat, and therefore they permit the boiler, not- 

 withstanding the proximity of water, to be unduly heated : the 

 consequence of which is, that the metal of which it consists is 

 burned, and greatly deteriorated in strength, or the earthy coat- 

 ing cracks, and allowing the water to come in contact with the 

 highly heated metal, a vast quantity of steam is suddenly formed, 

 or the water is even decomposed. The steam in one case, and the 

 gas in the other, gives rise to such a pressure as the boiler may be 

 unable to bear. The prevention of incrustration, besides removing 

 a serious source of danger, would have the effect of economising 

 fuel, by leaving the capacity of the metal for transmitting heat to 

 the boiler unimpaired. One method of preventing incrustrations, 

 is the removal of the earthy matters from the water before it is 

 introduced in the boiler ; this is difficult, and from circumstances 

 often impossible. Another method, is to render the earthy matters 

 harmless, by keeping them in a pulverulent state, and suspended 

 in the w T ater. An improvement on this method consists in arranging 

 a number of small thin plates within the boiler, in such a way as that 

 they over-lap, like the tiles on a roof, and form a thin space between 

 themselves and the walls of the boiler. The heat being imparted 

 directly to the water contained in this space, such a circulation is 

 produced, that any deposit of sediment on the boiler is impossible. 

 The sediment is, however, deposited on the plates ; but, not being 

 there exposed to a high temperature, it has no tendency to become 

 a compact mass. This arrangement is attended with another 

 advantage — the uniform and comparatively quiet disengagement of 

 the steam : not in the lower part of boiler, but at, or near the surface 

 of the fluid, on account of the presence of a large amount of solid 

 particles thrown up by the circulation caused by the wall of plates. 



Caloric Engines. — Whether steam or heated air is used, it is only 

 the vehicle for transmissions of the heat from the fuel to the work- 

 ing point, to be changed there into motion. Steam has unquestionable 

 advantages : air has, however, persevering and plausible advocates. 

 M. Bourget has recently introduced a modification of the caloric 

 engine which is attracting considerable attention. He heats the 

 air, after it has been condensed, by a system of tubes which are 



