218 Dr Fyfe on the Illuminating and Heating PoQver of 



gands. I have thought that it would be equally interesting to 

 extend the investigation to other forms of burners, such as 

 those with flat flames, and which are used without chimneys, 

 so as to shew their illuminating power compared with jets and 

 argands, and also the most economical way of using them. 

 The chief object, then, which I have had in view in the expe- 

 riments which I am now to relate, is to point out the illumi- 

 nating power of different kinds of burners as compared with 

 one another ; and I have thought it necessary to make these 

 preliminary observations, to shew the necessity of attending to 

 the circumstances which affect the consumpt and combustion 

 of the gas, by which the light afforded is so materially in- 

 fluenced. 



In conducting these experiments, I have invariably used the 

 coal-gas as supplied by the Gas Company. Though it varies 

 occasionally a little in its illuminating power, yet as the expe- 

 riments are merely comparative, and as the results of the 

 trials made on the same day are contrasted with each other, 

 this slight difiference does not affect them ; besides, it must be 

 borne in mind, that it is not my wish to fix with numerical 

 precision the amount of light afforded, but merely to ascer- 

 tain the comparative degrees of light given by the different 

 burners. 



In all of the trials I have used a single jet burner as my 

 standard; and to secure this giving forth always the same 

 light, it was connected with a gasometer, so adjusted as to 

 burn exactly one foot per hour, when the flame was five inches. 

 The gasometer employed for this purpose was on the usual 

 construction, — a copper vessel suspended in water, and coun- 

 terpoised by weights attached to cords passing over pulleys. 

 I am aware that it may be objected to this apparatus, that 

 as the gas-holder sinks in the water it becomes of less and 

 less weight, proportionally to the counterpoises, and that con- 

 sequently the pressure is not always the same. I was of 

 course aware of this, but I found on trial that, for short dis- 

 tances, the gas-holder moved, the difference in pressure was 

 trifling, particularly when the gas from it was used when the 

 gas-holder was not very much out of, or very much sunk in, 

 the water. Accordingly, I found that, for equal times, the 



