SOUNDS FROM ANIMATE NATURE. 323 



choly. This effect does not seem to be caused by asso- 

 ciation so much as by their peculiar cadence. 



The notes of these nocturnal pipers on very warm 

 evenings are in unison and accurately timed, as if they 

 were singing in concert. It is worthy of notice that they 

 always vary their keynote according to the temperature 

 of the atmosphere. They are evidently dependent on a 

 summer heat for their vivacity, and become sluggish and 

 torpid as the thermometer sinks below a certain point. 

 When the temperature is high they keep good time, sing- 

 ing shrilly and rapidly. As it sinks they take a lower 

 key and do not keep time together. When the thermom- 

 eter is not above sixty, their notes are very low, and 

 there are but few performers. 



