No. 396.] CHIRPING OF THE TREE CRICKET. 937 
Whether the same individual kept it up all night I am unable 
to say. For several evenings together and for several hours 
in the same evening I often got a series of chirps from what I 
suppose to have been a single individual in the same vine. 
As to the synchronism, it is true that several performers may 
be audible at the same time, but the intensity of sound increases 
rapidly as the individual is approached, so that when all are per- 
forming in the same zempo the nearest one gives the accent 
without all the others emitting their notes at exactly the same 
instant. 
Professor Dolbear’s formula is as follows : 
Let T = temperature in degrees Fahrenheit; M = number 
of chirps per minute; then 
N— 40 : ; J 
i= 50 P This would give 100 chirps for 65°. 
During some weeks this summer I have recorded a number of 
observations, amounting, with those taken in previous years, 
to fifty-six, and Mr. Faxon has kindly sent me a series taken 
by himself. : 
All three sets and formulz agree as to the rate of increase, 
t.e., four beats to a degree, but mine differ from the other two 
in making the absolute value either two or three degrees lower, 
as will be seen in the accompanying diagram, in which I have 
indicated the separate observations of Mr. Faxon and myself, 
as well as in the tables. 
It will be seen that in one-fifth the rule is exact for either 62° 
or 63° to the hundred, and in four-fifths the error is one degree 
or less. 
ONE HUNDRED CHIRPS CORRESPONDING TO | 62° 63° 
ERE E A N a o e II II 
Errr E OF NR ee ee aes 29 29 
TRON Or NR o” ee a ee 10 12 
Eror SR a o a a 5 3 
a a a a ge aN I I 
