Precursors of Internal Clock Theory: Hoagland and ‘The Chemical Basis of Our Sense of Time’

Abstract This article reviews a precursor of modern internal clock theory, the work of Hudson Hoagland from the 1930s proposing a ‘chemical clock’ as the basis for time judgements. Some of the background to Hoagland’s interest in the effect of temperature on timing is provided, as well as an explanation of the Arrhenius equation that Hoagland used to describe data. Hoagland claimed that timing was based on a specific underlying chemical process with an activation energy of 24 kcal. Some later studies of body temperature and time judgements are discussed. In general, the evidence that time judgements are affected by body temperature is strong, whereas evidence for a specific chemical clock of the type Hoagland suggested is very weak, with the few other studies that have used the Arrhenius equation failing to replicate Hoagland’s activation value.