220 Mr. F. W. Barrett on Sensitive Flames. 



lowed, erecting itself again at the next beat, only to be thrust 

 back as the sound again welled up ; thus a sort of breathing 

 flame was produced, the aspirations of which were strictly timed 

 to the sighing of the bell*. I next tried the action of a large 

 brass plate fixed at its centre to a stand. Throwing the plate 

 into vibration by means of a fiddle-bow, an energetic and large 

 divergence of the flame was obtained when the higher notes of 

 the plate were sounded. Holding the plate thus sounding close 

 to and parallel with the flame, a more strained and intense diver- 

 gence took place; the flame was in fact almost split in two, the 

 edges becoming denser and the central part a mere film of flame ; 

 but the divergence never reached down to the burner. Slowly 

 moving the plate so as to bring different parts in succession op- 

 posite the flame, the principal nodal lines could be traced as 

 easily as with sand. The intervals of rest in the vibrating plate 

 allowed the flame to raise itself up, and in its sluggish combus- 

 tion to stand, as it were, at ease, whilst the ventral segments 

 dragged it down to active burning and apparent attention. As 

 a lecture-illustration, this method of showing the higher vibra- 

 tions of a plate will be found useful where an audience is unable 

 to look down upon the plate to see the arrangement of sand on 

 the nodal lines. In this, as in all other experiments, the sur- 

 prising change in the brilliancy of the flame is a most striking 

 part of the phenomenon. 



The divergence of the flame is not due to the impact of trans- 

 lated puffs of air, but is an effect caused by sonorous vibrations. 

 This can be easily proved. For instance, standing a few yards 

 from the flame and bringing the hands forcibly together as if to 

 clap them, but stopping short of doing so, the flame remains 

 undivergent, the slightest clap, however, at once produces a 

 strong divergence. It is astonishing how far off a sound affects 

 the flame, notwithstanding the intervention of solid obstacles ; 

 one experiment will illustrate this. Whistling has a powerful 

 effect on the flame, especially so the shrill whistle obtained by 

 blowing into a key. Whilst I observed the flame, a friend 

 whistling in this way left the room wherein was the flame, 

 and, closing the door after him, slowly retreated upstairs; 

 though its action was enfeebled by closing the door, the flame 

 still continued to shrink at every whistle, and was visibly affected 

 even when the whistle was sounded where it could barely be 

 heard, in a closed apartment three stories away f. It -certainly is 



* I observe that Professor Leconte has previously noticed that his fish- 

 tail gas-flame exhibited pulsations in height exactly synchronous with the 

 audible beats of a musical instrument. 



\ Professor Tyndall, in his lecture, has shown that by slightly increasing 

 the pressure of the gas the flame is susceptible of even greater sensitiveness 

 than is shown in this experiment. 



