MECHANICS AND USEFUL ARTS. 29 



ample supply of oxygen is afforded, and all the heat generated is 

 saved and concentrated upon the lime." Herein is the principal feature 

 of Dr. Smith's invention. The invention is practically carried out for 

 railway (locomotive) lights the purpose for which it has thus far 

 been applied as follows : The burner is composed of four compound 

 jet tubes encircling a small cylinder of lime. A current of atmos- 

 pheric air, and one of coal-gas, is conveyed to each jet, and the two 

 allowed to mingle after leaving their respective jet orifices. The tube 

 conveying the stream of air, passes over several small gas burners, 

 which heat the air-tube to a high degree of heat, at a point near the 

 orifice of the tube, and by this device, the air current is intensely 

 heated before it reaches the jet and mingles with the jet of coal-gas. 

 The effect is, to produce the dazzling whiteness of the lime, peculiar 

 to the oxy-hydrogen light. When placed in the focus of a parabolic 

 reflector, such as are in present use upon locomotive engines, it is in- 

 creased to a ball of light twenty inches in diameter, or to the size of 

 the mirror. The flow of air and gas is reliably and simply controlled 

 by durable regulators and stop-cocks, within the lamp. Two gas- 

 holders containing air and coal-gas, respectively, under pressure, placed 

 under the engine, and communicating with the lamp by a small pipe 

 for each, carry twice or three times the requirements of a trip. These 

 receive their charge at the engine-houses, before starting, from two 

 stationary holders of larger dimensions, which are kept filled by a 

 small pump driven by the local power employed at those places. To 

 fill the holders on each locomotive occupies its engineer only from, 

 three to four minutes very much less time than is required for filling 

 and trimming an oil lamp. 



This light has within the past year been introduced upon the loco- 

 motive engines of the New York Central Railroad, and its efficacy 

 and great economy has been so fully demonstrated that the invention 

 may without doubt be ranked among the most useful and novel of the 

 year. 



IMPROVEMENTS IN TYPE-SETTING. 



Mr. Thomas Rooker has lately introduced into the Tribune office, N. 

 Y., type-cases with movable bottoms. In these cases, the bottoms may 

 always be kept conveniently full in composition, and in distribution 

 the bottoms may be lowered so as to receive a large quantity of type. 

 Mr. J. H. Tobitt, of New York, and Mr. A. H. Bailey, of Boston, have 

 also recently interested themselves, to introduce composite type, or the 

 plan of uniting two or more letters upon one body, so that by one lift 

 two or three letters are set up instead of one. Mr. Bailey's system of com- 

 binations is calculated to save from twenty to forty per cent, in com- 

 position. When it is considered that the word the forms six per cent, 

 of the language, and and about four, while many others exceed about 

 two per cent, the advantage of a combination system is evident. The 

 difficulty in the matter is as to how many and what combinations may 

 be used with profit. 



SCENE PAINTING. 



M. Foucault proposes to remedy certain defects in scenic arrange- 

 ments by the following means. At present, our mountains, towns, and 

 3* 



