208 C. Davison—Creeping of Soil-cap by Frost. 
If the different frosts be of different degrees of intensity and 
duration, the resulting line will be curved throughout its whole 
length, down to the lowest depth to which freezing has extended. 
But if, as in colder countries than ours, the frost last through nearly 
the whole winter, and in different winters do not vary greatly in its 
depth of penetration, then the resulting line will exhibit a more or 
less sharp bend at the average depth to which the frosts are felt, and 
above the bend they will be fairly straight. Mr. Kerr’s section 
(Fig. 1) seems to me to agree remarkably with this latter deduction ; 
and it will be observed also that the bends are all at nearly the same 
depth, which ought to be the case when the surface is not very 
uneven. 
5. The experimental evidence that I have been able to obtain, 
though less varied and complete than it might have been made in 
a colder country, is decidedly confirmatory of the above theory. 
The experiments were made in boxes inclined to the horizon, and in 
this respect the conditions were not quite natural, for the sides and 
bottom of the boxes, as well as the surface of the soil, were exposed 
to the cold. But the movements of the surface-particles near the 
middle of the boxes would not be affected by this. The method 
adopted, moreover, possesses several advantages, not the least being 
that the effects are more marked than they would be naturally, 
owing to the greater depth of frozen soil. — 
Two boxes, differing in form, were filled with damp, fairly 
compact, soil. The first (A) is, internally, 24; inches wide, 
2% inches deep, and, at the surface, 13 inches long; the lower end 
is horizontal, the upper vertical; and the inclination of the bottom 
of the box and the surface of the soil is 32°. A straight bar of 
wood is firmly screwed to upright supports at either end of the box, 
so that its lower edge is parallel to the surface of the soil and at a 
distance of 14 inches from it. The other box (B), rectangular in 
form, is, internally, 15+ inches long, six inches wide, and 63 inches 
deep; and is inclined at an angle of 27°. A straight bar of wood 
is also fixed to the box, with its lower edge parallel to the surface 
of the soil and one inch from it. Fine pencil-lines are ruled on 
both bars in several places, perpendicular and parallel to the lower 
edges; and serve as reference-lines for the measurement of the dis- 
placements. I will now give an example of the experiments made 
with each box. 
6. Experiment 1—(Box A). The index used to register the 
motion of the soil consists of a slab of sheet-lead, Zinch square, on 
two opposite sides of which are arms, one inch long and + inch wide. 
These are bent towards the centre of the slab, and, when they 
meet, bent again so as to be perpendicular to the slab. Part of a 
stout needle, 152; inches long, is bound tightly with strong silk 
between the projecting arms. The whole index weighs a little over 
three-fifths of an ounce. 
The index was placed so that the surface of the soil was level with 
the upper surface of the slab, and the soil was pressed closely all 
round it, so that there was no gap between the soil and the edges 
