Prof. A. M. Mayer's Researches in Acoustics. 379 



vibrations they gave when they were clamped at one end and 

 drawn from a horizontal position. On obtaining the ratio of 

 these numbers, I found that it coincided with the ratio exist- 

 ing between the numbers of vibrations of the forks to which 

 covibrated the fibrils of which these pine-rods were models. 



The consideration of the relations which these slender, taper- 

 ing, and pointed fibrils must have to the aerial pulses acting on 

 them, led me to discoveries in the physiology of audition which 

 I imagine are entirely new. If a sonorous wave falls upon one 

 of these fibrils so that its wave-front is at right angles to the 

 fibril, and hence the direction of the pulses in the wave are in 

 the direction of the fibril's length, the latter cannot be set in 

 vibration ; but if the vibrations in the wave are brought more 

 and more to bear athwart the fibril, it will vibrate with am- 

 plitudes increasing until it reaches its maximum swing of co- 

 vibration, when the wave-front is parallel to its length, and there- 

 fore the direction of the impulses on the wave are at right angles 

 to the fibril. These curious surmises I have confirmed by many 

 experiments made in the following manner. A fork which 

 causes a strong covibration in a certain fibril is brought near 

 the microscope, so that the axis of the resonant box is perpendi- 

 cular to the fibril, and its opening is toward the microscope. 

 The fibril in these circumstances enters into vigorous vibration 

 on sounding the fork ; but on moving the box round the 

 stage of the microscope so that the axis of the box always 

 points toward the fibril, the amplitudes of vibration of the fibril 

 gradually diminish; and when the axis of the box coincides 

 with the length of the fibril, and therefore the sonorous pulses 

 act on the fibril in the direction of its length, the fibril is abso- 

 lutely stationary, and even remains so when the fork in this 

 position is brought quite close to the microscope. These ob- 

 servations at once revealed to me another function of these 

 organs : for if, for the moment, we assume that the antennse are 

 really the organs which receive aerial vibrations and transmit 

 them to an auditory capsule, or rudimentary labyrinth, then 

 these insects must have the faculty of the perception of the 

 direction of sound more highly developed than in any other class 

 of animals. The following experiments will show the force of 

 this statement, and at the same time illustrate the manner in 

 which these insects determine the direction of a sonorous centre. 

 I placed under the microscope a live mosquito, and kept my at- 

 tention fixed upon a fibril which covibrated to the sound of a 

 tuning-fork which an assistant placed in unknown positions 

 around the microscope. I then rotated the stage of the instru- 

 ment until the fibril ceased to vibrate, and then drew a line on 

 a piece of paper under the microscope in the direction of the 



