ON INSECT SOUNDS 



23, 



with a film of iodised collodium, then dipped in a nitrate of silver 

 bath, exposed to light and dried. 



The prepared plate was arranged so as to be drawn steadily by 

 clockwork along another larger glass plate, and a knife point was 

 lixed in a frame so as to hang from above downwards, so that its 

 sharp point rested on the prepared surface and nearly perpendicular 

 to the plane of its motion. As often as the plate was set in motion 

 a tone of definite pitch was heard, the pitch appearing to depend 

 on the rapidity of movement of the glass plate and the weight or 

 pressure of the knife point. The same result would, of course, be 

 obtained if the knife point were moved on the glass. 



In order to be able to determine the number of incisions made in 

 a given time, and compare this with the pitch of the tone, the time 

 which passed during the production of the sound line was accurately 

 measured by means of a pendulum beating seconds, while at the 

 same time the height of the note was taken down. On counting 

 the tine incisions of the line, the result obtained was— -as expected — 

 that the numder corresponded tvith the number of vibrations of the tone 

 produced, small differences between the observed and the known 

 number of vibrations being accounted for by inevitable imperfections 

 of the experiment. The results of three trials are given in the 

 foUowins: table. 



Many audible sounds which are constantly referred to the 

 category of noises, prove on a closer examination to be undoubted 



