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gna §, No 11,, Man. 15. °56.] 
NOTES AND QUERIES, 
215 
Andrew Miller. — Lately 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, 1745;” 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, &e.” 
q 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. } 
Replies. 
STOCK FROST. 
(2"4 §. i. 151.) 
J. B. asks what stock frost can mean? but the 
remainder of his paragraph implies that he has 
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 
Sor 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 no 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 
