THE SENSITIVE FLAME. 17 



in the stem expresses the temperature of the 

 surrounding medium. 



The sensitive flame is another example of a 

 subject so impressionable that it indicates or ex- 

 presses very faint sounds or aerial vibrations. 

 The following quotation is from a lecture by Mr. 

 W. F. Barrett, delivered before the Royal Dublin 

 Society, January 8, 1868 : " The lecturer had re- 

 served for the conclusion a flame wonderfully sensi- 

 tive to the slightest noise. The burner which gave 

 this flame was formed of steatite, and consisted of 

 a single circular orifice, through which the gas was 

 forced from a large holder in the lecture-room, with 

 greater pressure than would be attained from the 

 main. The flame was now fully two feet in length ; 

 ' and observe,' said the lecturer, ' how delicate and 

 fragile a thing it appears to be ; for on the slightest 

 noise it drops down a foot. The jingling of this 

 bunch of keys, the crumpling of this paper, the 

 dropping of a small coin, are more than sufficient 

 utterly to break up its height and symmetry. This 

 flame makes no response to the vowels o, u, nor 

 to the labials, but it energetically responds to the 

 sibilants. Repeating the stanza 



"Kollon, rill, for ever ! 

 Eest not, lest thy wavelets, 

 Sheen as shining silver, 

 Shrink and sink to darkness ; " 



the flame is unmoved by the first line, but empha- 

 tically bobs at the sounds. "rest" and "lest," and 

 admirably suits its action to the words of the last 

 line, for, when shrinking, the light of the flame 



C 



