108 
rj:id on the simpxicity- of chemical apparatus. 
of the water beins: equal on all sides ; and as it 
is set in motion by the inclined plane of the 
screw, but little power is required to keep 
tl’.e wheel going, for the particles of fliii.ls 
move eavsily amongst themselves. The trough 
should be of an oval Ibrm. In order that no 
air may escape between the tube and the 
cylinder, a small strap of leather is fastened 
to tlm tube (which is fixed) to lap over the 
cylinder at P, fig. 1, and is kept dov\'n by a 
small w eiglit, hnng at the corner of each side, 
thus. No air, once enclosed or detached from 
the atmospiiere by the end Hof the spiral leaf 
being immersed in the water, can possibly 
escape but through the nose or tube. 
Fig. 3. Transverse sections of both ends of 
tiibp; and outline, as seen from its under side. 
The wheel may be made of any size requi- 
red. To ascertain the quantity of air dis- 
charged at each revolution first, find the 
whole contents of the cylinder, which we will 
suppose to be 14 feet in diatneter, by first 
finding the area of the base by multiplying 
the square of the diameter by "7854 ; then 
multiply the area by the length of 28 feet, thus, 
14 X 14=: 196 X *7854:1: 154, nearly, X 28— 
4312 contents of cylinder. Hut as it takes 
two revolutions to empty the cylinder, 4312 ~- 
2 — 2156 feet of air and water discharged at 
each revolution, 2156 2 ~ 1078 feet of air 
less 78 feet for internal cylinder, &c. = 1000 
cubic feet of air discharged at every revolution. 
If the motive-power, or the ^ elocity, cannot be 
easily regulated, a sling-valve may be made in 
the side of the tube C, 
Alfred T. J. Martin- 
Helston, Cornwall, June 6, 1835. 
P. S. — Since writing the above, a practical 
difficulty has been suggested fo me, viz., that 
(he pressure of air for smelting should be 2, 3, 
and even 41bs. to the square inch, equal to tlie 
pressure of a column of water about 7 feet 
high. I do not see how this desideratum can 
be obtained by the foregoing plan ; but still 
the invention may prove useful where large sup- 
plies of air are required without any consider- 
able pressure. — Mechanic’s Magazine, 1835. 
BRITISH ASSOCIATION. 
GEOLOGY AND GEOGRAPHY.— A 
memoir was read by Captain Denham, on the 
basins of tlie Mersey and Dee : — 
The paper was regarded by every one as of 
extreme value, and was received with great 
enthusiasm. We regret we can merely refer 
to it with great brevity, but we understand it 
will be speedily made public. He showed the 
difference between the horizontal impetus of 
running water, and its force when acting 
downwards by pressure. Channels had Deen 
opened to receive the tide, being more per- 
pendicular to its course, and yet the tide liad 
capriciously avoided them and no mud had 
been deposited. By many experiments and 
observations, he has determined, that while 
tlie high and low water levels are variable, 
the height of the mean tide or half tide is the 
same at all times ; a fact of the highest im- 
portance, both in a scientific and practical 
point of view. Let us hope that future ob- 
servations may speedily confirm tliis matter, 
and thus give us a secure standard as a base 
line for all onr measurements. 
DR. REID DELIVERED HIS VIEWS 
UPON A PLAN 1’KILD AT EDIN- 
BURGH, FOR 'I HE EXTENSION OF 
THE STUDY OF PHYSICS.-Ile pro- 
posed to have large classes formed for observ- 
ing chemical experiments, and that nothing 
should be employed in these experiments which 
were not easily procurable by every person. A 
bit of glass as glaziers throw away, a piece 
of charcoal, and a blow-pipe, would be in- 
struments enough with which to make from 
one hundred to one thousand experiments, 
and these would illustrate the essential ope- 
rations of chemistry. Bythismearrs a pecu- 
liar knowledge would be obtained, and tlie 
mode of conducting an examination on a small 
scale. Dr. Reid here made some experiments 
on a small piece of glass, and afterwards on 
paper, showing the formation of crystal.s, 
&c., and the effects were as distinctly marK- 
ed as could be desired. He recommended 
that the pu[)ils should write down on paper, at 
the time, the changes observed by them during 
the experiments. Dr. Reid then made some 
beautiful experiments, by applying tests to dif- 
ferent liquids and solids. He took some lead 
ore, and adding nitric acid to it, myriads of lit- 
tle globules were at once reduced from the ore, 
and fell upon the paper. At the term ination 
of each experiment the persons present were 
handed the specimens. The lecturer said, 
that a common beer-bottle with a tube, and 
another bottle I’or a receiver, would answer 
for the preparation of gases, and the conduct- 
ing of operations on a small scale was the- 
better to the student, as the substances pas- 
sing frcm one state to another were distinctly 
seen in a simple apparatus. Fron» calcula- 
tions made in different places, he found tliat 
from 2/. to 5L would provide apparatus and 
materials sufficient to show many thousand 
experiments. The great object was to render 
this department of Liovvledge accessible to 
all persons ; and, as to the time its fitudy 
should be commenced, he (Dr, Reid) would 
say from three to nine years of age would 
rot be too early. This species of information 
was easier ofacquisition than thatof language. 
The greatest difficulty with children was to 
arrest their attention, on account of the live- 
liness of their sensations, and obstruct sub- 
jects were not sufficient to excite interest. 
Objects in external nature they observed, and 
were ready to attend to any instruction afford- 
ed in reference to them. The lecturer then 
noticed the necessity of persons devoting a 
short time to informing themselves of the 
principal practical results ef chemistry in re- 
liition to the knowledge of the purity of water, 
the component parts of agricultural materi- 
als, &c. This species of knowledge would be 
of the highest utility to the emigrant, and by 
imparting it to the natives of the district in 
which lie located himself, he Mould be ele- 
vating the character of liis own countrymen, 
and receiving the friendship and support of 
strangers. 
