32 Drs Christison and Turner on the Construction of 
No one who has paid attention to the statements contained in the fore- 
going parts of this paper, will have any difficulty in conceiving whence these 
extraordinary discrepancies have originated. 
The results of our experiments have differed, of course, with the quality 
of the respective gases. When the oil -gas was ‘of inferior, and the coal-gas of 
superior quality, when, for example, the specific gravity of the former was 
818, and that of the latter 653, the relative illuminating power, according to 
some of our earliest experiments (on which, however, we do not place much 
reliance), was only 100 to about 140. When the oil- gas was of the best, and 
the coal-gas of average quality, the specific gravity being 605 and 1110, the 
proportion was 100 to 260. If the same oil-gas was compared with bad coal- 
gas, such as that used by Mr Dewey, and by Messrs Phillips and Faraday, 
the specific gravity of which did not much exceed 400, the proportion would 
probably be so high as one to four. 
The following is a detailed account of the experiments on which we are 
disposed to place the greatest reliance. The first series was made a few weeks 
ago, at a time when we were fully acquainted with all the circumstances which 
affect the light. A 5-inch jqt of coal-gas burnt through an aperture a 28th of 
an inch in diameter, was compared with a 4-inch jet of oil-gas, burnt through 
an aperture of a 45th of an inch, the specific gravities being 578 and 910. In 
one experiment, the distances on Count IlumfoM’s photometer were 64 § in- 
ches for the coal-gas, and 69 for the oil-gas ; while the 10th part of a cubic 
foot of the former was consumed in 367 seconds, and of the latter in 685. The 
result gives a proportion of 100 : 218.6. In another experiment, the distan- 
ces were 62| for the coal-gas, and 67 \ for the oil-gas, and the consumption 355 
and 685, from which a proportion is procured of 100 to 223^. 
The experiments were performed in like manner with Argand burners, that 
for coal-gas having 14 holes a 32d of an inch in diameter*, on a circle of T %th 
radius, and that for oil-gas having 20 holes of a 50th on the same circle. The 
coal-gas flame was fully 2§ in height, the oil -gas flame 2|, being the most favour- 
able elevations for such burners. In the first experiment, the distances were 62 
for the coal-gas, and 7 6 for the oil-gas, and a 5th of a cubic foot of the former was 
consumed in 212 seconds, and of the latter in 314. The proportional light, as 
calculated from these numbers, is 100 to 223. This experiment was repeated 
in the following manner. The former distances being preserved, and the lights 
extinguished, the flame of the coal-gas burner was kindled again, and adjusted, 
so that the expenditure was exactly the same as before, and the flame of the 
oil-gas burner was then regulated, so that the shadows were alike. The re- 
spective elevations of the flames proved to be the same as before, and the ex- 
penditures were„212" and 307" These data give a proportion of 100 to 217* 
The mean of the four experiments is 100 to 220, or 1 to 2 \ nearly. 
Professor Leslie’s photometer gave a proportion somewhat higher. In the first 
experiment with the Argand burners, it fell 17 degrees at the distance of 6£ 
inches from the centre of the coal-gas flame ; and, in the second experiment with 
the same burners, it fell 27 degrees at the same distance from the middle of the 
Glasgow Burner, No. 2. 
