162 



Dr. Andrew Fyfe on the Comparative Value of 



not give a flame of sufficient height ; indeed the same is some- 

 times the case with jet 45. For these reasons, I now prefer the 

 jet 40, .because, while it gives a very steady flame at 5 inches, 



the water-column in the gauge is much longer than when a jet 



33 or 35 is used ; and thus, any slight inaccuracy, in noting the 

 pressure, leads to a smaller error in the results, than when the 

 same inaccuracy is committed, in noting the pressure when the 



water column is not so long. 



The following is the result of trials made with the different 



jets I have mentioned : 



Trials with Flame. 





4 Inch 



es. 



1 



5 Inch 



es. 



Jets. 



Pressure in 



1 foot burned 



I Jets. 



Pressure in 



1 foot burned 



lOOths of inch. 



in in u tea. 



lOOths of inch. 



minutes. 







i ft 







/ It 



25 



15 



75 35 



30 



50 



65 25 



30 



30 



75 30 



33 



68 



64 25 



33 



44 



75 4L 



35 



110 



65 



40 



90 



72 55 



40 



120 



63 40 



45 



no 



72 30 



45 



155 



64 40 



50 



196 



1 



75 



1 







On viewing the results above given, it will be observed, that 

 the times for the consumption of 1 foot are very nearly the same. 

 Had the difference followed any regular gradation, then we might 

 have supposed that it was occasioned by the difference in the 

 size of the aperture in the jet : but as it does not do so, we may, 

 I think, safely conclude, that, with jets of different apertures, and 

 with flames of the same height, the quantity of the same gas 

 consumed in the same way is the same ; or that the times for 

 equal consumptions are the same. That this is really the case is 

 still farther proved by taking a small jet of gas, of given height 

 of flame, and marking the consumption by metre ; then remov- 

 ing the jet from the socket, which is left open, and consuming 

 the gas from it ; the quantity in the same time, will be found to 

 be the same. Or, burn the gas from the latter, with a flame of 

 such a height as can be measured with any degree of accuracy : 

 then introduce a jet, and burn the gas with the same height of 

 flame ; the quantities consumed are the same, or as nearly so as 

 can be expected from trials of the kind, where it is difficult to 

 measure accurately the length of flame. Hence, most probably, 

 the cause of the difference of time in the table given ; that dif- 

 ference having been occasioned by the flame in some of the trials 

 having been a very little too high or too low, in the cases where 

 the difference is greatest. Even that difference, especially in the 

 last table, the experiments of which were repeated again and 

 again, with slightly varying results, is only V 20". This shews 



peated 

 fixed 



the flame, and again 



