Different kinds of Coal for the purpose of Illumination. 271 



From the foregoing table, it is evident, I think, that the 

 mode of finding the consumpt by the pressure is sufficiently 

 accurate for all practical purposes. I mean, of course, mere- 

 ly with the view of finding the durability of gases, as I do 

 not propose it as a method for superseding the use of metres, 

 to ascertain the quantity of gas consumed by different indi- 

 viduals. I must mention, however, that in one or two in- 

 stances, the observed pressure did not give the consumpt, as 

 indicated by the metre : whether this was owing to a peculi- 

 arity in the gas, or to inaccuracy in noting the results, I do 

 not know. At the time that the expei'iments were perform- 

 ed, the i-esults were merely marked down, and the calcula- 

 tions were made afterwards ; and after discovering the want 

 of correspondence, I had not then an opportunity of repeats 

 ing the trials with the same coal, which was very remark- 

 uljle for affording a gas of very high illuminating power. 

 This was the more to be regretted, as the gas being at one 



