234 ^^ INSECT SOUNDS. 



as a sound, or it may be by contact of antennae. If a true speech 

 be claimed, it must be objected that the psychology of insects has 

 not yet been placed on the only possible basis of brain physiology, 

 on which such an hypothesis can be founded. 



I now proceed to the consideration of certain phys-ical phenomena 

 explanatory of the various insect sounds. 



The following account of an experimental enquiry insti- 

 tuted by Professor D. H. Landois on the shrill tones of insects, 

 is taken from an interesting little volume published recently by 

 this gentleman, and entitled **^ Animal Voices.'' 



When the point or sharp edge of a penknife is drawn over the 

 surface of a highly polished plate of metal or glass, a shrill musical 

 sound is heard. On examining the track made by the penknife 

 with a lens or under a microscope, it will be found to consist of a 

 number of minute incisions situate very close together^ which, with 

 their interspaces, are disposed with a regularity proportioned to the 

 greater or less uniformity of the tone heard. The astonishing 

 minuteness of these incisions will be best understood from the fact 

 that the experimentors counted in one case 150 in the space of one 

 millimeter. They are obviously produced by the intermittent 

 descent of the knife edge upon the polished metal surface, and the 

 number of cuts equals that of the shocks or beats which produce 

 the sound. 



In the Annals of Physics and Chemistry (Poggendorf) Vol. cl., 

 page 565, tables 7 and 9, Professor Landois has published a long 

 series of experiments, accompanied by phototypes from photographs 

 of a number of these sound lines , probably the first instance of 

 sound being photographically represented. The plates which he 

 found best for his experiments were made of thick glass well 

 polished on the surface, which was variously prepareti. In some 

 cases a solution of gum arabic was poured over the surface in a 

 very thin layer, and this, when well dried, was blackened over the 

 flame of a petroleum lamp. In others the solution was blackened 

 by addition of indian ink 3 in others, again, the surface was covered 



