INSECT VAKIETY. 209 



lethargic Cockney Moth [Biston Hirtaria), of seasonable appear- 

 ance in the London parks, when imprisoned in a box, will thus 

 invariably respond for a minute at evening- to the successive 

 mural tremors arising from a passing rumble of wheels in the 

 street below. Then if two stout-bodied moths, especially if male 

 and female of the same species, be enclosed in chip-boxes and 

 placed in too near proximity, they, as is well known, I imagine, 

 to every patron of the lamp-posts and sugar-pots, beat alternately 

 and in quick succession, despoiling themselves of their pleasant 

 nap. Now the fact of these insects raising their emotions in 

 alternation, or consecutively to certain sounds, seems to establish 

 this as a provision for sexual communication, and as an intima- 

 tion of jealousy ; while the ardency of its utterance when the 

 opposite sexes are approximated, indicates a love-call that repro- 

 duces in miniature the strutting, wing-drumming, and rustling 

 of the males of the turkey and grouse at the pairing time. 



The popular science of acoustics has not failed to direct its 

 researches to the investigation of the atmospheric sounds of 

 insects, which it aspires to gauge both in pitch and as to the 

 component wing-beats ; and for this purpose three instruments 

 are available — the wheel of Savart, the syren, and the graphic 

 cylinder. The wheel of Savart is simply an ordinary toothed 

 wheel, which, when scraped over a simple piece of cardboard, 

 gives a whizzing sound that varies in height with the celerity of 

 revolution, the stroke of each tooth being considei-ed to impart 

 a simple vibration to the said cardboard. In the case of the 

 syren, an invention ascribed to Cagniard Latour, a Frenchman, 

 and so called because it can be made to sing beneath water — 

 air is forced by a pair of bellows through holes in a flat and 

 horizontal plate, which are covered and opened by similar 

 orifices revolving in a circular disc ; so that the faster the 

 motion the quicker the jets of air escape, each puff being con- 

 sidered as forming a simple atmospheric vibration. Lastly, the 

 graphic method is an ordinary revolving cylinder covered with 

 soot, which, when applied to a vibrating object, writes the beats 

 in wavy scratches on its surface, the celerity of the turning 

 handle being employed to decipher the resulting superscription. 



Even if we suppose the correctness of the indications 

 afforded by these instruments, which must be in itself a matter 

 o 



