Different kinds of Coal for the purpose of Illumination. 269 



The results, by experiment and by calculation, above given, 

 so very nearly correspond with one another, that I think we 

 are warranted in concluding, that the pressui-e corresponds 

 with the specific gravity, and that consequently the specific 

 gravity may be ascertained by the pressure, when the gases are 

 consumed under similar circumstances ; having of course pre- 

 viously determined the specific gravity of a gas known to re- 

 quire a certain pressure for its consumpt. Consequently 

 the specific gravities being ascertained experimentally, the 

 consumpts may be known ; these being, the times for equal 

 consumpts, as the roots of the specific gravities, and the con- 

 sumpts in equal times, inversely as these roots. 



Having established these positions, the next object I had 

 in view was to ascertain, by a more extended series of trials, 

 whether an indication of the consumpt of gases, in different 

 places, could thus be obtained, without having recourse to a 

 metre, which, to an experimenter, carrying one from place 

 to place, is troublesome. It at first occurred to me that this 

 might be done by ascertaining the specific gravity ; but this 

 also must be a troublesome process, and unless ascertained 

 with accuracy, would not tend to accurate results, especially 

 in a hurried visit to different gas-works, where the height of 

 the barometer cannot be always observed. After numerous 

 trials, I at last determined to have recourse to the pressure- 

 gauge, consuming the gas with a given height of flame, and 

 always from the same burner. For this purpose, I used 

 in my first trials the platinum-jet foi-merly alluded to, with 

 an aperture of }^ of an inch, furnished with a scale for 



VOL. XLV. NO. XC. — OCTOBER 1848. T 



