34 Drs Christison and Turner on the Construction of 
910, the actual light, compared with that of coal-gas, in the same way as in the 
experiment alluded to, would have exceeded 6 to 5, which was the proportion 
he procured. A very slight additional correction on this account, would give 
exactly the proportion assigned by us above. 
The condensation caused by chlorine in the coal and oil gas used in our last 
experiments, was 13 and 37. This method of estimating the illuminating 
power is therefore in the present instance erroneous. 
The only other experiments we shall mention, were made last October, at 
a time when we were not sufficiently acquainted with the circumstances which 
modify the light of the gases. Although not strictly correct, therefore, in 
some particulars, they will nevertheless give a good approximative result. 
The specific gravities of the gases were 1110 and 605, and the condensation by 
chlorine 46 and 16. A 5-holed coal-gas burner (Edin. No. 1.) with a 3-inch 
flame, consuming a 10th of a cubic foot in 186 seconds, was compared with a 15- 
holed oil-gas burner, having a flame of 2 \ inches, and consuming a 10th of a 
foot in 375 seconds. The distances were 56 for the coal-gas, and 614 for the 
oil-gas. These data give a proportion of 100 to 243. A 10-holed coal-gas 
burner (Edin. No. 2.) with a 3-inch flame, consuming a 10th of a foot in 120 
seconds, was compared with a 20-holed oil-gas burner, having a flame of 2| 
inches, and consuming a 10th of a foot in 215 seconds. The distances were 
56 and 674 > an d the proportional light is therefore 100 to 260. In these two 
experiments, the coal-gas burners were not of the best construction ; but, on 
the other hand, the flames of the oil-gas burner were not at the most favour- 
able elevation. The mean of the two observations, or the proportion of 100 
to 250, is probably very near, and certainly not beyond, the truth. 
On the subject of comparative experiments regarding the illuminating 
power of the gases, we have only farther to remark, that the easiest and most 
correct mode of making them, is by using jets of a regulated length. It ap- 
pears from some of our experiments formerly noticed, that all illuminating 
gases give nearly the same additional light, by combining their jets in proper 
Argand burners. Consequently, the proportion that holds in the case of jets 
will apply equally well to Argand burners. Now, experiments with the for- 
mer are not liable to so many fallacies as those made with the latter. In fact, 
we have only to attend to the diameter of the holes, the length of the flames, 
the steadiness of the pressure on the gasometer, and the accurate measurement 
of the expenditure, and adjusting of the shadows. 
We have now concluded the account of our experiments, ac- 
cording to the plan laid down at the commencement of the pa- 
per. It was not originally our intention to make any remarks 
on the relative advantages of the two gases, in a general point of 
view. But as the subject has lately led to a long Parliamentary 
investigation, and as very erroneous notions prevail on some 
matters which have engaged a share of our attention, it may be 
well to notice it briefly. 
The question of the relative advantages of oil and coal gas re- 
