381 



Art. XVII. Miscel/aneuus Intelligence, 

 I. Mechanical Science. 



§ The Arts, Agricultural Economy, S)C. 



I. Improvement of Oil Lamps. — MM. Arago and Fresnel 

 have lately applied the principle of Count Rumford's concentric 

 or co-lateral meshes to the improvement of lamps, intended 

 either for light-houses or theatres, or for other uses where a 

 strong bright clear light is wanted. In order to obviate the 

 difficulty which was formerly found to arise from the carboniza- 

 tion of the wick by the great heat occasioned at the summit of 

 the burner, the oil was made to flow over at the mesh, in the 

 manner proposed and adopted by M. Carcel ; and in thus keep- 

 ing the flame at the top of the wick, a full, clear and steady 

 combustion was obtained. Many circumstances require atten- 

 tion in making these lamps produce their best effect ; as the 

 space between the meshes, the size of the air canals, the height 

 of the chimney, the magnitude of the reservoir, Sj-c. When 

 perfect, the experiments made with them, though they seemed 

 to indicate a slight degree of saving in the oil required to 

 produce a certain quantity of light with lamps having two wicks, 

 yet they did not, as a general result, with three and four wicks, 

 justify the opinions of Count Rumford; and the quantity of light 

 produced, was about the same as what would have been given 

 by the same quantity of oil burned in other economical me- 

 thods. The principal advantage is the po%ver of concentrating 

 all the light into one focus, so that when advantageously 

 placed, as on the centre of a light-house furnished with lens, 

 the greatest quantity may pass from one point through the 

 lenses. The light of these lamps is very regular ; for, after 

 twelve or thirteen hours' burning, it does not diminish more 

 than one-fifth, — at least such was the result with a four- 

 wicked lamp placed in the focus of a large lens. The quantity 

 of oil allowed to flow over at the wi k, should be at least equal 

 to that which is burned. It is not ; pparently injured, and is to 

 be returned into the reservoir. In [Jace of the apparatus em- 

 ployed by M. Carcel, to make the oil rise to the wick, MM. 

 Arago and Fresnel placed the reserv oir of oil above the height 

 of the burner; and then, by an open moveable tube, which 

 passed into it from the air, the level up to which the oil was 

 required to flow was easily regulated. — Annalcs tie Chimic, xvi, 

 p. 377. 



2. Coal- Oil Parish-Lamps. — It is now some time since the 

 volatile oil, obtained by distilling coal and coal-tar, has been 

 applied in place of animal oil, in producing light. F/irgc 

 quantities of this fluid are j^reparcd at once from the coal in 



