Davy's Experiments on the Frictional Development of Heat

Abstract

IN NATURE for March 9, 1935 (p. 359), Prof. Andrade directed attention to the persistent textbook errors concerning Davy's experiments on the fractional development of heat, pointing out, among other things, that the much-quoted experiment on the melting of two pieces of ice by rubbing them together was not carried out in a vacuum. It may be of some interest to inquire how Davy produced and maintained the vacuum for the first experiment, in which a gunlock was fired, and for the third experiment, in which wax was melted by the heat developed by the friction of a wheel rotated by clockwork against the plate carrying the wax. Davy gives no details of his vacuum apparatus, but refers to the “exhausted receiver” of an “air-pump”. In the first experiment the trigger of the gunlock was snapped, he says, by this means: “A slight iron wire was affixed to the trigger, brought through a hole made in the centre of the stand [supporting the receiver], and cemented into the hole with wax, so as to exclude entirely atmospheric air from the receiver”¹. Presumably the same device was used in the third experiment to start the clockwork.