Prof. F. Clowes. 



[Feb. 2, 



In cases where caps of equal height are given for different percent- 

 ages of gas, it must be understood that the higher percentage gives a 

 more dense and sharply denned cap than the lower percentage 

 does. 



The general conclusions drawn from these measurements, and from 

 experience derived from working with the different lamps, are the 

 following : 



1. The indications of the Pieler lamp begin at the lowest limit of 



0'25 per cent., but quickly become too great to be utilised. 

 The thread-like tip extending above the flame for several inches 

 in pure air must not be mistaken for a cap, but it is scarcely 

 distinguishable from the cap given by O25 per cent, of gas. 



This lamp suffers under the disadvantage that much of the 

 feeble light of the caps is lost by the obstruction of the gauze : 

 the gauze also frequently presents a bright reflecting surface 

 behind the flame, and this renders the observation of the 

 cap impossible. All the other lamps in use are free from the 

 interference due to the gauze, and if their glasses are black- 

 ened, as already described, they become well suited for the 

 observation of caps. 



2. The Ashworth benzoline lamp begins its indications doubtfully 



at 0-5 per cent., the cap thus produced being more distinct, but 

 not greater in height, than the mantle of the flame seen in gas- 

 free air. 



But starting with certainty with an indication of 1 per cent., 



