il6 SYMPATHETIC VIBRATIONS. 



led by the observations of Hensen, has made similar 

 experiments with the mosquito, the male of which has 

 beautifully feathered antenna?. He fastened one down 

 on a glass slide, and then sounded a series of tuning- 

 forks. With an Ut^ fork of 512 vibrations per second 

 he found that some of the hairs were thrown into 

 vigorous movement, while others remained nearly 

 stationary. The lower (Uts) and higher (Utg) harmo- 

 nics of Ut4 also caused more vibration than any 

 intermediate notes. These hairs, then, are specially 

 tuned so as to respond to vibrations numbering 512 

 per second. Other hairs vibrated to other notes, 

 extending through the middle and next higher octave 

 of the piano. Mayer then made large wooden models 

 of these hairs, and, on counting the number of vibra- 

 tions they made when they were clamped at one end 

 and then drawn on one side, he found that it " coincided 

 with the ratio existing between the numbers of vibrations 

 of the forks to which co-vibrated the fibrils." It is 

 interesting that the hum of the female gnat corresponds 

 nearly to this note, and would consequently set the 

 hairs in vibration. 



Moreover, those auditory hairs are most affected 

 which are at right angles to the direction from which 

 the sound comes. Hence, from the position of the 

 antennae and the hairs, a sound wdll act most intensely 

 if it is directly in front of the head. Suppose, then, 

 a male gnat hears the hum of a female at some little 

 distance. Perhaps the sound affects one antenna more 

 than the other. He turns his head until the two 

 antennae are equally affected, and is thus able to 

 direct his flight straight towards the female. 



The auditory organs of insects, then, are situated in 



