234 STUDIES IN THE FIELD AND FOREST. 



unison with the August pipers, varying their tone in 

 the same manner with the variations of temperature. 

 But the diurnal insects do not keep time so well as 

 those which are the particular subject of my observa- 

 tions. 



When the mercury stands at about 70°, a few insects 

 may be heard singing out of tune. Their time is also 

 more imperfect, and is equal to about two notes to a 

 second. When the weather is as cold as 60° — the 

 average temperature of the evenings in August and 

 September — the greater number will be heard on the 

 key of ^Jlat. Their time, however, in this state of the 

 weather, is Very imperfect, and a great many will be 

 heard singing out of tune, some a tone or a semitone 

 higher, and others as much lower than B fiat. I 

 attribute this difference to the different degrees of 

 warmth which they may find, according as they are 

 more or less protected from the external air. If one, 

 for example, be confined in a room in the house, when 

 the outer air is cool, the one confined will chirp several 

 notes higher than any that are singing out of doors. 

 When the temperature is very warm, there is probably 

 more uniformity of heat in all places and situations, 

 than when it is cooler. Often, on a sudden change of 

 temperature from warm to cool, some individuals that 

 happen to be in a little snug retreat that still preserves 

 the early heat of the day, will sing more briskly and on 

 a higher key than others. When the weather is below 

 60°, all the insects sing very feebly, without regard to 

 time or tune ; those only that happen to be protected 

 under the warm projection of a roof, or the trunk of a 

 tree, chirping on a higher key than the rest, and with 

 more vivacity. 



I have no doubt that with an accurate thermometer, 



