The Kennet is one of those rivers that exhibit the phenomenon of ice forming in the bottom, and we were informed here by the Earl of Craven's fisherman, that, in severe winters, the ice forms with such rapidity in those parts of the river that are shallow, and where, of course, the stream is rapid, that, in one night, a complete dam has been formed across the stream, of such a height as to throw the water over the adjoining banks. The water thus thrown over also freezes, and the consequence would be, a complete inundation of the valley above, if the fishermen did not take effectual means to break up this dam. It is observed that, when the bottom of the river is frozen, one good effect is the result, and this is, that, when it thaws, the pieces of ice, which float up from the bottom, bring all the weeds with them; thus thoroughly cleaning the river. Observing a circular pond of stagnant water close by the margin of the Kennet, we asked the fisherman whether he had observed what took place in this pond when the river froze at the bottom. He perfectly understood the question, and answered that this pond, and all other stagnant water, froze at top. Some years ago, Mr. T. A. Knight made an attempt to explain the cause of running water freezing first at the bottom, in the Transactions of the Royal Society; and the same interesting subject has been discussed by various correspondents in our Mag. Nat. Hist., v. 91. 303. 395. 770.; but the phenomenon has only lately been explained satisfactorily in Jameson's Philosophical Journal. It is there shown that it proceeds from the motion of the water, mixing the frozen laminï¾µ at top with the water below, till the whole mass becomes cooled down to the freezing point, when crystallisation takes place, beginning at the bottom and sides, as it does in the case of crystallisation of salts. Every gardener may prove the truth of this theory, if he will take the trouble of keeping the water of a small pond in motion, by stirring it while freezing. Possibly, if thorns were dragged through the water of canals full of weeds, by men on the banks of both sides, during the frosts of winter, when labour is cheap, the weeds, when a thaw should take place, might be separated from the soil at the bottom of the pond or canal more cheaply and effectually than they could by mowing. This might be tried on a small scale. (To be continued.)
