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Cricket Chirps: Nature's Thermometer

Posted by Diego Fonstad
Diego Fonstad
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on Tuesday, 09 August 2011
in Great Explanations

Teachable Moment: I'm not sure what I like more about this idea: the practical nature of it or the fact that the correlation between temperature and cricket chirp rate was documented by one of the inventors of the radio telephone.

From Farmer's Almanac:

Did you know that you can tell the temperature by counting the chirps of a cricket? It's true! Here's the formula:

To convert cricket chirps to degrees Fahrenheit, count number of chirps in 14 seconds then add 40 to get temperature.

Example: 30 chirps + 40 = 70° F

To convert cricket chirps to degrees Celsius, count number of chirps in 25 seconds, divide by 3, then add 4 to get temperature.

Example: 48 chirps /(divided by) 3 + 4 = 20° C

From Wikipedia:

Dolbear's law states the relationship between the air temperature and the rate at which snowy tree crickets (Oecanthus fultoni, a tree cricket) chirp[1]. It was formulated by Amos Dolbear and published in 1897 in an article called The Cricket as a Thermometer. The chirping of the more common field crickets is not as reliably correlated to temperature — their chirping rate varies depending on other factors such as age and mating success. In many cases, though, the Dolbear's formula is a close enough approximation for field crickets, too.

Dolbear expressed the relationship as the following formula which provides a way to estimate the temperature TF in degrees Fahrenheit from the number of chirps per minute N:

T_F = 50 + left ( frac{N-40}{4} right ).

This formula is accurate to within a degree or so when applied to the chirping of the field cricket.

Counting can be sped up by simplifying the formula and counting the number of chirps produced in 15 seconds (N'):

,T_F = 40 + N'

Reformulated to give the temperature in degrees Celsius(°C), it is:

T_C = 10 + left ( frac{N-40}{7} right ).

A shortcut method for degrees Celsius is to count the number of chirps in 8 seconds (N'') and add 5 (This is fairly accurate between 5 and 30°C):

,T_C = 5 + N''

The above formulae are expressed in terms of integers to make them easier to remember — they are not intended to be exact.

References: http://www.almanac.com/cricket-chirps-temperature-thermometer
http://www.srh.noaa.gov/epz/?n=wxcalc_cricketconvert
http://en.wikipedia.org/wiki/Dolbear%27s_Law

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