Royal Sociely. 385 
receiver in a pneumatic trough. This mode, consisting of two 
operations, is liable to mistake, as the vessel the air is passed 
under should be sufficiently large to receive the whole of the air 
at once; otherwise it would require two or three operations, 
which would render it more doubtful. As some healthy subjects 
inspire above a gallon of air, the jar should hold five quarts at 
least, and this is above the rate of common recipients: besides, 
it requires some practice and dexterity to convey gaseous fluids 
from one vessel to another, and it is also a most unpleasant ope- 
ration. These objections induced me to try other means. I 
then had a tin apparatus, made upon the principle of the pneu- 
matic bellows, as described in Mr. Watts’s pneumatic apparatus. 
The difficulty of having this so nicely balanced as to give the ex- 
act proportion, obliged me to make further efforts, for the fric- 
tion of the inverted cylinder prevented the necessary sensibility 
of the instrument. 
“<The machine I use at present is a glass jar, which is in- 
verted into a pneumatic trough ; it holds two gallons of water, 
and is graduated by a scale, divided into pints and half-pints, 
unto six quarts. ‘The trough is filled with water. up to number 
four, so that two quarts of water stand in the bottom of the jar 
when it is ready for use; at the upper part of the jar a tube 
passes, in which is fixed a stop cork; about two inches above 
the cork the tube turns at a right angle, and is carried horizon- 
tally for near six inches; it is then flattened into a mouth-piece, 
which enables the person using the machine to close the lips 
about it with greater facility.” 
A selection of cases in which the pulmometer was applied 
with decided advantages closes Dr. Kentish’s performance, which 
cannot fail to be read with interest. As his establishment in- 
creases additional improvements will no doubt continue to be 
made to it, and its advantages will consequently be more widely 
diffused, and more duly appreciated. The scheme is of course 
still in its infancy; but in the mean time great praise is due to 
Dr. Kentish for the zeal and public spirit with which he has set 
the establishment on foot. 
LXXXIV. Proceedings of Learned Societies. 
ROYAL SOCIETY. 
April 28, Tue conclusion of Dr. Brewster’s paper on Mother 
of Pearl was read. The author considers the optical pheno- 
mena of mother of pearl very different from those of all other 
bodies: in some of his experiments the thickness of the pearl 
plates did not produce any change on the phenomena, in others 
Vol, 43. No, 193, May 1814, Bb some 
