erally disappears, being
carried away by the current or dissolved by the thaw.

The last time that I remarked this phenomenon, was in a stream of
the river Aire, near Bradford, in Yorkshire, on the 1st of
January, 1814. This instance did not precisely accord with what I
have stated to be the usual circumstances of the case, as the
frost then had existed several days without any previous
appearance of this kind; but there were several indications of
approaching change of temperature, and the day following there was
a partial thaw attended with rain, the wind having veered from
north-west to south-west. This thaw, however, did not continue
long, and was succeeded by a frost which surpassed all within my
recollection in severity and duration. Yet during the whole of the
period, though the thermometer often stood below 18 degrees
Fahrenheit, and the estuary of the Tees several miles below
Stockton, where the spring-tides rise from twelve to eighteen
feet, was for two months frozen over, so as to allow the passage
of a loaded waggon, I could never perceive a particle of ice
adhering to the rock or gravel, in the bed of the small and rapid
river Leven in Cleveland, where I then resided. This circumstance
seems decisively to prove that the phenomenon does not merely
depend on an intensity of cold.

I confess I am unable to frame any hypotheses respecting the
above-mentioned facts which would not be liable to numerous and
formidable objections. The immediate cause of the formation of the
ice seems to be a rapid diminution of the temperature in the stone
or gravel in the bed of the river, connected with the sudden
changes in the state of the atmosphere, but it does not seem very
easy to explain the precise nature of this connection.

We may easily conceive that by a sudden change from a state of
thaw to an intense frost attended by a strong wind, the whole body
of water in a river may become quickly cooled, and consequently
diminish the temperature of the stone or gravel over which it
flows; but to suppose that water which is not itself at freezing-
point is capable of reducing the substances in contact with it by
means of a continual application of successive particles so far
_beneath_ that temperature as in process of time to convert the
contiguous water to ice, seems not to accord very well with the
usually received theory of the equilibrium of caloric. However,
the fact that the quantity of ice thus produced is always g