851 



the addition of an element in combination, as the velocity of oxygen 

 is increased, by combining it with carbon without change of volume, 

 in carbonic acid gas. 



It did not enter into the plan of the author to investigate the pass- 

 age of gases through tubes of great diameter, and to solve pneuma- 

 tic problems of actual occurrence, such as those offered in the dis- 

 tribution of coal-gas by pipes. But he states that the results must 

 be similar, with truly elastic gases such as air and earburetted hy- 

 drogen, whether the tubes be capillary or several inches in diameter, 

 provided the length of the tube be not less than 4-000 times its dia- 

 meter, as in the long glass capillaries of his experiments. The small 

 propulsive pressure applied to coal-gas is also favourable to transpi- 

 ration, as well as the great length of the mains ; and he therefore 

 woul4 expect the distribution of coal-gas in cities to exemplify ap- 

 proximately the laws of gaseous transpiration. The velocity of coal- 

 gas should be 1*575, that of air being 1, under the same pressure. 

 And with a constant propulsive pressure in the gasometer, the flow 

 of gas should increase in volume with a rise of the barometer or with 

 a fall in temperature, directly in proportion to the increase of its 

 density from either of these causes. 



These laws, it will be observed, are entirely different from those 

 which direct the passage of gases through an aperture in a thin plate, 

 or their flow into a vacuum as it is usually said, and could not be 

 deduced, like the latter, from our speculative ideas respecting the 

 elastic fluids. 



11. "On the Automatic Registration of Magnetometers and Me- 

 teorological Instruments by Photography." — No. III. By Charles 

 Brooke, M.B., F.R.S. 



The author describes the construction of an apparatus for regis- 

 tering the variation of the thermometer and psychrometer on one 

 sheet of paper. As in the apparatus for registering the vertical force 

 magnetometer, described in a former paper, the photographic paper 

 is placed between two concentric cylinders, placed with the axis ver- 

 tical, and carried round, on a revolving plate or turn-table by the 

 hour-hand of a time-piece, which makes half a revolution in twenty- 

 four hours; thus each half of the paper presents a record of the 

 variation of one instrument during twenty-four hours. The scales 

 of the instruments are continuously impressed on the paper by placing 

 fine wires opposite each degree across the aperture through w^hich 

 the light falls on the stem ; the light transmitted by the empty bore 

 is intercepted by these wires, and the darkened portion of the paper 

 is marked by a series of parallel pale lines corresponding to each 

 degree : thus the distortion of the scale arising from the varying di- 

 rection of the pencils of light is corrected. Every tenth degree is 

 marked by a coarser wire, and therefore a broader line, as also the 

 points 32°, 54°, 76°, 98° ; one at least of these points will occur on 

 each register, and the position of the extra broad line serves to iden- 

 tify the part of the scale to which the register relates. 



An alteration in the mode of adjusting the wick of the camphine 

 lamps described in a former paper is mentioned, by which the chance 



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