A uditory Apparatus of the Culex mosquito. 357 



from the various resonant boxes, 1 adopted the plan of sounding 

 with ii bow each fork with the greatest intensity I could obtain. 

 1 think that it is to be regretted that Kiinig did not adhere 

 to the form of fork with inclined prunr/s as formerly made by 

 Warloye; for with such forks one can always reproduce the 

 same initial intensity of vibration by separating the prongs by 

 means of the same cylindrical rod, which is drawn between 

 them. Experiments similar to those already given revealed a 

 Hbril tuned to such perfect unison with Ut^ that it vibrated 

 through 18 divisions of the micrometer, or '15 millira., while 

 its amplitude of vibration was only 3 divisions when Ut^ was 

 sounded. Other fibrils responded to other notes; so that I infer 

 from my experiments on about a dozen mosquitos that their 

 fibrils are tuned to sounds extending through the middle and 

 next higher octave of the piano. 



To subject to a severe test the supposition I now entertained, 

 that the fibrils were tuned to various periods of vibration, I mea- 

 sured with great care the lengths and diameters of two fibrils, 

 one of which vibrated strongly to Uty, tlie other as powerfully 

 to Ut^; and from these measures I constructed in homogeneous 

 pine-wood two gigantic models of the fibrils, the one corre- 

 sponding to the Utg fibril being about 1 metre long. After a 

 little practice I succeeded in courting readily the number of 

 vibrations they gave wheu 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 fibi-ils 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 



the intensity, we have the amount produced by the vibration with its entire 

 intensity. Then means can be devised by which the aerial vibration pro- 

 duced by this fork cau ahvays be reproduced with the same intensity. 

 This intensity, expressed in fraction of Joule's unit, is stamped upon the 

 apparatus, which ever afterward serves as a true measure for obtaining the 

 intensities of the vibrations of all simple sounds having the same pitch as 

 itself. The same operation can be performed on other forks of different 

 pitch ; and so a series of intensities of ditferent periods of vibration is ob- 

 tained expressed in a corresponding series of fractions of Joule's unit. 

 Recent experiments have given - — ? — - of a Joule's unit as the approxi- 

 mate dynamic equivalent of ten seconds of aerial vibrations produced by 

 an Utj fork set in motion by intermittent electromagnetic action and placed 

 before a resonator. 



Ann. ct* Mag. N. Hist. Ser. 4. Vol. xv. 25 



