

166 



Dr. Andrew Fyfe on the Comparative Value, fy 



A screen fitted up in this way, stretched on a frame, with a 

 holder for the light at the back, and with another holder in front 

 for the other light, is all that is required : of course, if gases are 

 to be tried, the holder in front must be furnished with a jet of 

 the diameter previously fixed on, and with a flexible tube to be 

 connected with the gas-pipe. This holder can be made to move 

 backwards and forwards on a scale, graduated to inches, with 

 their corresponding squares ; or to lights of candles, as may be 

 thought proper. To make the apparatus more complete, the gas- 

 jet can be furnished with the pressure-gauge, which I have re- 

 commended for ascertaining the durability ; and thus, by the two 

 together, the value of gases may be quickly ascertained. 



This mode of trying the illuminating power will be found very 

 useful ; not that I prefer it to the chlorine test, for by the lat- 

 ter, ail gases can be compared with a standard of unity, the illu- 

 minating power being just as the condensation ; but because the 

 former is easily managed, especially by those not practised to 



Could a truly uniform source of light 

 be procured, and, by general consent, be fixed on, as that for the 

 back of the screen, then the light from gases, or indeed from 

 other sources, could be compared with it ; but as yet, we are not 

 so far as I am aware, in possession of such a light. 



With the use of the screen now described, I was anxious to 

 repeat the trials made, with the view of ascertaining the light for 



equal consumptions of gases by different burners ; an account of 



work with water-troughs. 



which was published in the Transactions of the Society for 1842, 

 because I have again and again heard the accuracy of these re- 

 sults called in question. In conducting the trials, I had, as before, 

 recourse to an experimental metre, to ascertain the consumption, 

 and made use of a gas-jet flame, always of the same height, and 

 always at the same distance from the back of the screen. Each 

 series of trials being conducted in one day, the gas was, of course, 

 of the same quality for each day, by which a uniform transmis- 

 sion of light from behind was obtained. 



The following are the average results : 



BrjRNERS. 



Jel — Hauie 5 inches, . . 



Small Fishtail, . . . 



Largv Fishtail, . . , 



Small Batwing, . . . 



Large Batwing, . . . 



Argand, 40 holes, . . . 



Consumption 



in 60 



minutes. 



1 foot. 



1-1)8 

 2-60 



3-00 



4 60 

 4-50 



100 



2-89 

 4-00 



440 



8-40 



7-84 



Ugbt Tor 



equal con- 

 sumptions 



1-00 



J-45 



1-46 

 187 



1 74 



pape 



was 



the most 



profitable way of consuming gas is by the Argand, properly con- 

 structed ; in other words, that" for equal consumptions, the great- 

 est amount of light is given by the Argand ; next by the bat wing ; 



