The first paper describes a simple instrument, called a “cryopedometer,” for measuring the depth of frost in the ground and the second gives some observations recorded by the instrument at the Parc Saint-Maur observatory.

The instrument Footnote * consists of a series of small open-ended glass capillary tubes, 4 mm. in diameter and 20 mm. long, containing water, which are mounted horizontally at 6 mm. centres on a notched wooden rod. The rod slides into a tube set vertically in the ground. The capillary tubes, in which the water becomes frozen, are readily seen when the rod is withdrawn.

The observations in the second paper show that the ground froze twice to a depth of 23–24 cm. during the winter. The slow initial melting of the frozen zone from above and below and the final sudden disappearance of the frost are to be noted.

The simplicity of the instrument suggests that it might be very useful for expedition work and in other conditions which do not warrant employing sensitive potentiometers or other instruments.

A close sliding fit between the wooden rod and the ground tube is essential to prevent convection between adjacent capillary tubes. The reviewer is constructing an instrument as the author suggests, out of plastics, for use during the 1947–48 winter.