INWIT TELLING TEMPERATURE WITH CRICKETS
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Telling Temperature with Crickets
by Vincent Mallette
Copyright © 2000 Inwit Publishing, Inc.
An Activity Involving
J CRICKETS J
Did you know that a cricket can tell you the temperature? Pretty accurately, too, better than you can guess. Count the number of chirps in 15 seconds
and add 40. The result will be the Fahrenheit temperature. This is known as Dolbearís Law. (Can you work it out for the Celsius temperature scale?
Answer at end.)
Dolbearís Law tells us immediately when a cricket is "too cold to chirp." What is that temperature?
The grasshopper, closely related to the cricket, is the only creature which can emit a sound which it cannot hear! 1
With whom or what is it communicating?
In 1913 a high-school teacher named Johann Regan used a new-fangled device, the telephone, to determine if the cricketís chirp is a mating call: male
crickets were induced to chirp into a phone, and female crickets, in another room, headed for the receiver. This literal "mating call"
confirmed the hypothesis. 2
Little metal toys called crickets, which emit a chirping sound when squeezed, were of invaluable help to Allied parachutists and secret agents behind
German lines in World War II. City-bred soldiers, who didnít know how to make bird calls, used the metal crickets to find each other and group up after
a parachute drop, without alerting nearby German sentries.
There is a special name for the sound which crickets make: stridulation. This funny word comes from the Latin "stridulus," which means
"squeaky." Incidentally, crickets make this chirping sound by rubbing together little "teeth" on their wings. Only male crickets make
this sound, but among some related insects the females do as well.
A. E. Dolbear (1837-1910) was a physics professor at Tufts College. He was also twice mayor of Bethany, West Virginia. 3
1 The World Book Encyclopedia, 1988 Edition (Chicago: World Book Inc., 1988) Vol. 18, p. 600.
Specifically, grasshoppers can emit a sound of 100,000 Hz, but they can only hear up to 15,000 Hz
2 The Timetables of Science by Alexander Hellemans and Bryan Bunch (New York: Simon and Schuster, 1988), pp. 422-424
3 Dolbear formulated his law about 1896. Strictly speaking, he intended it to apply only to "white tree" or "snowy tree" crickets, Oecanthus
niveus. There are other laws for other chirping insects. For example, the formula for the katydid is T = 60 + [(n - 19)/3], where n is the number of
chirps in one minute [http://naturalpartners.org/InsectZoo/Students/orthoptera.html]. But Dolbear's crickets are said to be the most accurate temperature
indicating insects. A later naturalist claimed that the formula would be even more accurate if you changed the 40 to 39. Why don't you go out in the
field and make some measurements to see if Dolbear's Law should be tuned up a little? It has also been suggested to count the chirps in 14 seconds and
add 40 to that. What different results would these formulas give you? Assume a rate of 15 chirps in 15 seconds and make your calculations based on that.
For further reading: Cricketology by Michael Elsohn Ross (Minneapolis: Carolrhoda Books, 1996).
Count the number of chirps
in 8 1/3 seconds
and add 4.444
(Not so convenient, is it!)
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