Playing cricket
Question: A friend of mine assures me you can tell the temperature by
listening to the chirping of crickets. Is this true and, if so, how?
Answer: There is an old rule that the ambient temperature in degrees
Fahrenheit is equal to the number of cricket chirps in 15 seconds plus 40. The
ambient temperature in Celsius is roughly equal to the number of cricket chirps
in 8 seconds plus 5.
Thus, if a cricket is heard to chirp 112 times in one minute, the temperature
is approximately 68 °F or 20 °C.
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Experiments that have been carried out on the snowy tree cricket (
Oecanthus fultoni) suggest that the chirp rate is regulated by the rate of
one or more metabolic reactions in the cricket. These experimental results are
consistent with an exponential dependence on the cricket’s absolute
temperature.
This type of behaviour is described by the equation that was deduced by
Swedish chemist Svante August Arrhenius in 1889 to explain the relationship
between chemical reaction rates and temperature.
The rule described above, then, is a linear approximation to the exponential
dependence and is usually good to within a degree or two over the range of
temperatures at which crickets chirp.
Robert Hopkins
Houston, Texas
Answer: It has been observed that the average frequency of chirping of a
snowy tree cricket is 100 per minute at 17.3°C, 126 per minute at 20.3°C
and 178 per minute at 25°C. If a graph of this data is drawn, it is
clear that as the temperature increases, so does the chirping of the
crickets.
Therefore, the following formula can be applied to the data: the temperature
in degrees Fahrenheit equals 0.8 multiplied by the number of chirps in 15
seconds plus 42. This temperature can then be converted into Celsius by
subtracting 32, multiplying by 5 and dividing by 9.
So yes, it is possible to calculate the temperature by listening to the
chirping of crickets.
Michael Hadcroft
Glasgow
An Arrhenius plot for the chirping of crickets features on page 66
of To Light Such a Candle by Keith J. Laidler (Oxford University Press,
1998). Interesting biological applications of the Arrhenius law are discussed in
the Journal of Chemical Education (p 343, vol 49)—Ed
Seeing double
Question: My sister, who is quite short-sighted, pointed out that when she
looks in a mirror, the image of a distant object looks just as out of focus as
the actual object when viewed directly. Why is this?
Answer: The reason why the object is just as blurry to your short-sighted
sister is because the light has to travel the distance to the mirror and then
from the mirror to her eye. You are looking at the sum of the two distances, not
at the mirror itself. A simple experiment to prove this is to get a small
sticker and place it at eye level on the mirror. Note that looking at yourself,
at an object behind you, and at the sticker on the mirror all require you to
adjust the focus of your eyes accordingly.
It appears as if the object behind you is actually behind the mirror, and
exactly that same distance away from it. Therefore the distance from the eye of
the viewer equals the distance of the viewer from the mirror plus the distance
of the object from the mirror.
Anybody checking their appearance in a mirror would do well to bear this
principle in mind. It could save you from acute embarrassment.
Remember that you are looking at yourself from twice the distance to the
mirror. If you want to check for blemishes make sure that you get closer to the
mirror. You’ll be able to spot things that you wouldn’t normally notice but
other people would . . .
Peter Milroy
Sydney
Answer: The answer will be quite simple to anyone who is acquainted with
photography. When focusing on an object in a mirror, one has to calculate the
effective distance by measuring the distance from the camera to the mirror and
adding it to the distance from the mirror to the object.
An autofocus camera will only read the distance to the mirror and therefore
the focusing distance needs to be set manually.
John Worthington
Stourbridge, West Midlands
This week’s questions
Molton core: Most items that are defrosted in a microwave thaw from the
outside in, sometimes resulting in a frozen core and heated exterior. Can any
reader suggest why butter should be the exception to this rule, sometimes
producing a liquid core while the outside remains firm and cool?
Robert Brayley-Hodgetts
Hove, Sussex
Dreamtime: Do people who were born blind dream? And if they do, do they “see”
in their dreams?
A. Chanemougasoundaram
Shimla, India