The loud crickets chirping in unison tonight reminded me of A. E. Dolbear’s observation that crickets can tell you the current temperature.  According to his classic 1881 communication:

T = 50 + (N-40)/4

where N is the number of field cricket chirps per minute, and T is the temperature in Fahrenheit.  An easier to remember equivalent is

T = N + 40

where, in this case, N is the number of chirps in 15 seconds.

I gave it a try tonight.  I counted 91.7 ± 2.1 chirps per minute, yielding a calculated temperature of 62.9 ± 0.5 degrees.  The actual reading on the thermometer outside?  61 degrees.  Pretty good accuracy, and no instrumentation required.

Bonus science trivia:  All nearby crickets of the same species will synchronize their chirping — despite the fact that the males are actually competing with each other for mates.

Extra bonus science trivia: The chirping rate of crickets (and many activities of cold blooded creatures) actually follows the Arrhenius equation for the temperature dependence of chemical reaction rates.  The chirping rate is a function of temperature because of the underlying biochemical reactions that give the cricket the energy it needs to chirp.

[Reposted from 8/16/13.  Outside my window, tonight’s chirp count was 104/min, or 66 degrees, and the actual thermometer reading was 64.]