236 ON INSECT SOUNDS. 



musical tones which may be distinguished with accuracy, but which 

 cease rapidly and as suddenly change for other tones. 



Now the phenomena of friction sounds and tones in the 

 Articulata are exactly analogous. In crabs, spiders, beetles, 

 crickets, &c., the fine notches which are found on their various file 

 or rasp-like organs, correspond with the marks on the sound lines 

 of the plates experimented upon, and over these file-notched organs 

 some sharp edge, belonging to some other part of the body, is 

 moved backwards and forwards. The tone produced bears exact 

 relation to the fineness of the notches, and the rapidity with which 

 the moving part of the apparatus is driven. It is observed, for 

 instance, that when the movements of the thighs of the grasshopper 

 begin rather slowly, th^ " s.r.r." tone is deeper than when the 

 motion is more rapid ; and the finer the notches, or the more rapid 

 the movements, so much more acute are the tones given out by the 

 cricket, beetles, bugs, &c. 



If the number of notches and the length of the file be known, 

 and also the time occupied by the movement of the organs, the 

 pitch of the tone produced by the insect can be easily reckoned. 

 And, conversely, other unknown quantities may be found as, e.g. 

 the number of notches on the file can be reckoned from the data of 

 pitch of tone, length of file, and time of motion. 



If we call I. the length of the sound line or notched organ, 



n. the number of notches to i millimeter. =t?3- inch, 

 t. the time occupied by friction on the notched line 



along I mm. of its length, 

 s. the number of vibrations of the note, 



we obtain the formula ^—=s, the application of which to the 



sounds made by insects is of practical importance. Thus, for 

 instance, let it be required to determine the pitch of sound 

 produced by the Ceramhyx (capricorn beetle). Professor Landois 

 measured the length of the notched ridge on the meso-pectus of a 

 male Ceramhyx moschatm, the length of whose whole body was 



