1822] 
at pleasure, was pointed out. The 
dilatation of the chest in man, and the 
other mammalia, by the muscular ac- 
tion of the diaphragm, and by the 
movements of the ribs, during inspira- 
tion, and its contraction during exspi- 
ration, were fully explained, and 
partly illustrated by a machine, which 
exemplified the effects of the motion of 
the diaphragm. This part of the sub- 
ject was concluded by an account of 
the peculiar mechanism of respiration 
in birds, by which the same air is 
made to pass twice through the lungs, 
before it is finally ejected from the 
system ; being received into large cells, 
which inclose all the principal organs, 
and even pervade the muscles, and 
subcutaneous membrane. 
Dr. Roget next gave a brief ac- 
count of the chemical changes ef- 
fected in the blood, which is exposed 
to the action of the air during respi- 
ration. Our knowledge of these 
changes, he remarked, was not so 
much derived from the direct analysis 
of that flujd in its different states of 
venous and arterial, as from the in- 
ferences necessarily to be drawn from 
the changes found to have occurred in 
the air by its passage through the 
lungs. These changes consist in the 
disappearance of a quantity of oxygen, 
and the addition of a corresponding 
quantity of carbonic acid, and of wa- 
tery vapour. The redundant carbo- 
naceous principle which accumulates 
in venous blood in the course of the 
circulation, is thus discharged in the 
lungs by its combination with oxygen, 
and the blood is restored to the vivify- 
ing arterial qualities. The analogies 
between this process, and that of slow 
combustion, were pointed out, and cx- 
tended to the phenomena of the high 
temperature which so many animals 
maintainabove the surrounding media, 
and which establishes so striking a 
distinction between warm and colil- 
blooded animals, more especially re- 
markable among the larger inhabitants 
of the ocean. 
THE SOCIETY OF ARTS. 
Messrs. W. Bishop and Co. of Nant 
y Moch, near Holywell, have obtained 
the Isis gold medal, for a paper on 
the porcelain-clay and bubhr-stone of 
Halkin Mountain, Flintshire. 
The qualities which fit a stone for 
prinding corn, especially wheat, are . 
rdnegs, to prevent it as muchas pos- 
sible from wearing down by the constant 
Proceedings of Public Societies. 
147 
friction to which it is exposed, a cer- 
tain degree of tenacity, to prevent the 
grinding surface from scaling or 
chipping off, and a cellular structure, 
in order to increase the quantity of 
cutting surface, the walls of the cells 
being at the same time thick enough to 
resist the strain upon them. _ All the 
fine flour required for the supply of the 
metropolis, and of the other large 
towns in this island, is prepared by 
means of millstones of French buhr. 
In the year 1816, Mr. Thomas 
Hooson, of Flint, observed on Halkin 
mountain a bed of remarkably fine 
porcelain clay, which, on exposure to 
the potters’ fires, was found to assume 
a more delicate whiteness than any 
substance of a similar nature hitherto 
found in this kingdom ; and seeing also 
other substances which he thought 
likely to be useful to the potters, he 
obtained from Earl Grosvenor a lease 
of all clays, rocks, and stones (except 
limestone), within his lordship’s liber- 
ties; and, subsequently, with a view 
to an extended trade, formed his pre- 
sent partnership with Mr. Richard 
Fynney, Mr. William Bishop, and 
Mr. James Whitehead, established 
under the firm of the “ Welch Com- 
pany at Nant y Moch, near Holywell,” 
where they have erected works for pre- 
paring the clay, which is called “‘ Cam- 
bria,” for sale, by separating it froma 
white siliceous sand and rock, with 
which the bed is found mixed toa depth 
at present unknown, but which has 
been proved as deep as twenty-six 
yards. The sand, when separated, is 
used for glass-making; and the white 
siliceous rock, now called “ Rock 
Cambria,” is ground down and used 
in the composition of china and earth- 
enware, instead of ground flint, or is 
mixed with it. Lor this process of 
grinding, several thousand tons of 
chert are annually consumed in the 
Staffordshire potteries, and much is 
supplied from Halkin mountain. In 
quarrying this chert, some of it in the 
state of vesicular entrochital horn- 
stone was raised, which, when uscd 
together with common chert, indicated 
such a superiority by its expeditious 
grinding and its little wear, and 
showed such a proximity in appear- 
ance (after having been worked) to the 
French buhr, that its use for grinding 
wheat was considered probable; and 
this led to the first application of the 
vesicolar Halkin rock as a buhr-stone. 
Halkin Mountain (called “ Alehene” 
at 
