Having had occasion in the course of my work to investigate some of the properties of the mercurial thermometer, I have obtained a series of results which are comprised in a memoir now submitted to the Society. A brief summary of these is given in the following abstract.

1. After describing a simple method of calibrating a thermometer, I give a detailed proof (following Pierre) that the calibration unit gradually undergoes a slight diminution in value. In the course of five years this may amount, in a new thermometer, to as much as ·21 per cent. The 0°–100° interval, therefore, requires periodic verification.