Dolbear's Law: T(°F) = 50 + (chirps per 14 sec)
In 1897, physicist Amos Dolbear published the relationship between cricket chirp rate and temperature. Crickets are ectothermic — their metabolism speeds up with heat, making them chirp faster. The snowy tree cricket is most reliable: count chirps in 14 seconds and add 50 to get °F. For field crickets: count chirps in 15 seconds and add 37. The relationship is remarkably accurate within 55-100°F. Below 55°F, crickets rarely chirp. The underlying chemistry: muscle contraction rates follow the Arrhenius equation, doubling roughly every 10°C increase. This is a real-world example of how temperature affects biological reaction rates.