Page:Notes and Queries - Series 2 - Volume 1.djvu/223

. NO 11., MAR. 15. '56.]

NOTES AND QUERIES.

215

Andrew Miller. Lntely I have become pos- sessed of a fine copy of an old and rather rare print of" Oliver Cromwell, Lord Protector of the Commonwealth of England, Scotland, and Ire- land; and John Lambert, Lieutenant-General of his Forces." As appears on the face of it, " An- drew Miller fecit, Dublin, 1Y45 ; " and it was "sold by Mich. Ford, painter, in Ann Street, near Dawson Street." Can you refer me to any source for particulars of Andrew Miller and his works, and likewise of Michael Ford ? Pilking- ton gives no information.

The painting is stated to have been "in the collection of George Rochfort, Esq.," and the plate is " dedicated to the Right Honourable Ri- chard, Lord Viscount Molesworth, Lieutenant- General of His Majesty's Forces, and Master- General of the Ordnance of Ireland, &c."

ABHBA.

[Short notices of both Andrew Miller and Michael Ford, and their engravings, will be found in Bryan's Dictionary of Painters, and in Strutt's Biog. Dictionary.']

STOCK FROST. (2 nd S. 1. 151.)

J. B. asks what stock frost can mean ? but the remainder of his paragraph implies that he lias heard it used for water frozen at the bottom of a river, whilst its surface remained unfrozen, in- stances of which have been mentioned to him, but he disbelieved them, and requests to be en- lightened on the subject.

If he wishes for instances in which this pheno- menon has been noticed by careful observers, and further, to know what philosophers have sup- posed to be the causes of its production, he may find a paper on the subject from the pen of that eminent philosopher, lately deceased, M. Arago, in The Annuaire for 1833; or he may see a trans- lation of it in the Edinburgh New Philosophical Journal, vol. xv. p. 123. ; or if neither of these are within his reach, there is a carefully drawn- up paper in the Transactions of the Royal Society for 1835, p. 329., by the Rev. James Farquhar- son, of Alford, Aberdeenshire, the disappearance of whose name from the list of F.R.S. implies that he also is dead.

J. R.'s disbelief is probably the effect of his being well aware of that wisely and mercifully ordained anomaly in the law regulating the effect of cold upon water, by which the surface ordinarily freezes first, and the fish are saved from being encased in masses of ice.

The general rule is this, that whereas heat counteracts the attracting force which particles of the same body exercise upon each other, a diminu-

tion of their heat will allow that force to operate more powerfully ; so that if the body be in a liquid state it will collapse, as we see spirits of wine, or quicksilver, shrink into less compass in a thermometer under any chilling influence ; and when the particles are thus more closely packed together, the weight of any given bulk of the fluid must necessarily be thereby increased. Hence when the surface of any piece of water is chilled by a stream of cold wind, each drop of water^col- lapsing becomes heavier than the unchilled water on which it floats, and will sink into it, and be replaced on the surface by it. If this law con- tinued to operate, the succession of sinking cold drops would make the bottom the coldest ; and the water at the bottom would be first frozen, and the whole mass above it gradually, if the chilling in- fluence from the wind were adequately continued. But if we had also a water thermometer standing with the other two at temperate, or 55, and if all the three were immersed in a frigorific mix- ture, we should see the liquid sink, from the col- lapsing in each of them, till they reached 7 above freezing point ; after which the water would sink no more, whilst the other two would be going down ; and when the spirits of wine "and quicksilver fell below 32, the water, turning into ice, would rise considerably in the stem, if it did not burst the bulb.

The corresponding result upon a piece of water will be, that the drops forming its surface, when chilled down to 39, will collapse no more, and therefore sink no more, but constitute a surface of ice, and the chilling of the lower portion of the water will ho longer be continued by the previous process.

The formation of ice at the bottom, while the surface is unfrozen, is at variance with the regular irregularity imposed on the effect of chilling water, and can only take place from disturbing causes. " Such ice," says Mr. Farquharson, " never ap- proaches the firmness and solidity of surface ice. It has nearly the aspect of the aggregated masses of snow seen floating in rivers during a heavy fall of snow, but. is of much firmer consistence than they." He proposes to call it "ground gru," because the Scotch call floating snow gru. Its most frequent occurrence is in the beds of rapid rocky streams, where the freezing water of the surface is some- times dashed down to the bottom, and where the asperities of the bottom facilitate the formation of crystals of ice, as saturated saline solutions form crystals more readily on rough bodies. Such are two of the causes to which Arago attributes this anomalous production. The mill-wheels, as men- tioned to J. B., may produce similar effects. Mr. F. has found that the ground- gru is also formed on a muddy bottom in cauliflower-shaped clusters, but only " when the sky was clear, or very nearly clear," so as to be favourable to the radiation of