106 
ANALYTICAL THEORY OF HYDRODYNAMICS. 
terrupted by withdrawing the wires from the 
cups of mercury, and the result is, that the 
greatest part of the adhering iron drops oft' 
and falls in the space between the two dishes. 
'J'he next dish now comes under the magnets, 
the communication is restored, and a fresh 
discharge fi om the buckets takes place, and 
so the process is continued. 
Some iron constantly adheres to the magnets, 
but this is found of no inconvenience, as it 
bears but a small proportion to the total 
quantity separated. 
The author has bad an imperfect apparatus 
of the sort above described at work for some 
time, and has found it to answer ; and sug- 
gests the application of electro-magnets_ for 
somewhat an analagous objects in various 
manufactures. He particularly mentions 
needle and other dry grinding. — Proceedings of 
the British Association: Loud, and Edinb* 
Phil, Mag., vol. vii.,p.305. 
ON A NEW ROTATIVE STEAM- 
ENGINE OF INCREASED POWER, 
CONSTRUCTED BY MR. SIMS, BY 
JOHN 1 AYLOR, ESQ., F. R. S., TREAS. 
G. S., &c, — It is very well known to those 
who have observed the duty of steam-engines 
employed in the mines of Cornwall, that an 
enormous difference has existed between those 
which raise vvater by a reciprocating motion, 
and those which for other purposes have that 
motion converted into a rotative one by the 
intervention of a crank. The cause of this 
difference has often been speculated upon, 
but has not, I believe, been well explained : 
it is important in an economical point of view, 
as while in the pumping engines sixty millions 
pounds are commonly raised one foot by each 
bushel of coal consumed, the rotative engines 
for stamping ores have seldom raised more 
than twenty millions, and those for winding 
up the ores from under ground are found to 
be even far below this in effect. 
Now, it should be observed, that the pump- 
ing engines are at present universally, I 
believe, single engines, that is to say, re- 
ceiving the steam from the boiler on one side 
of the piston only, the principle of working 
double, as it is called, which was introduced 
by Mr. Watt, having been for some time 
discarded; and in these single engines the 
method of working high pressure steam ex- 
pansively, which we owe to Mr. Woolf, has 
long been used with the greatest advantage, 
I’he rotative engines in Cornwall, like all 
others which are used for manufacturing 
purposes, are double engines, and receive the 
steam alternately above and below the piston ; 
and though attempts have been made to work 
them expansively, these attempts have not 
been very successful. 
The object of my present address to you, is 
to notice an engine which has lately been con- 
structed for a mine in which I am interested, 
which is a rotative one for stamping tin ores, 
and which, when I visited the mine a few 
days since*^, was calculated to be performing 
* Mr Taylor’s letter is dated ‘‘ Bedford Row, 
Oct. 12 , 1835.”— A. T. 
a duty of about sixty millions, or nearly equal 
to the average of the better class of recipro- 
cating engines, and nearly three times, as 
much as tlie best rotative engines have hi- 
therto done. 
I wish to call the attention of persons con- 
cerned in the use of steam-engines to this 
fact, because if it should be found that this 
rate of duty can be maintained, a very great 
improvement may take place in all such as 
are most generally employed. 
This engine is at work at the Charles Town 
united mines, near St. Austle ; it was erected 
for us under the direction of Mr. Sims, an 
engineer of great experience in Cornwall. It 
differs from the general construction, in 
being a single engine, having the beam load- 
ed at the outer end ; and the rotatory motion 
of the crank is rendered almost completely 
uniform by the assistance of the flywheels. 
It works nearly as expansively as the pump- 
ing-engines. 
It was predicted, T understand, before the 
engine went to work, that a steady rotative 
motion could not be produced in this way, 
and some believed that the crank would 
never pass the centre ; I can, however, bear 
witness that the action is extremely good, and 
will, I believe, by a little alteration in the 
weight and diameter of the fly-wheels, be 
made perfect ; and as it must be an object to 
save at least one half the fuel ordinarily con- 
sumed, I point it out as deserving attention 
and inquiry. I have desired that its per- 
formance may be legularly reported in the 
monthly duty papers. 
I am informed by Captain Thomas Lean, 
who reports the duty of most of the engines 
in Cornwall, that this is not the first construc- 
tion of the kind, but that a similar one was 
erected formerly at VVheal-Vor tin-mine, by 
Mr. Peter Godfrey, and that it then surpassed 
in duty any other stamping engine of its day, 
but that for some reason it never attracted 
much notice. 
Mr. Sim.s is constructing a w'inding-engine 
for the same mine, on a similar principle. — 
Lond. Sc Edinb. Phil. Mag., vol. vii., 
p. 369. 
ON THE SIMULTANEOUS VIBRA- 
TIONS OF A CYLINDRICAL TUBE 
AND THE COLUMN OF AIR CON- 
TAINED IN IT. BY J’HE REV. 
JAMES CHALLIS.— Mr. Challis, in his re- 
port on the Analytical Theory of Hydro- 
dynamics, and elsewhere, has expressed the 
opinion that to complete the theory of musical 
vibrations in a cylindrical tube, it is necessary 
to take into account the vibrations of the tube 
itself. 
In this communication he states some results 
which he has arrived at theoretically, respect- 
ing the kind of influence the tube will exert 
on the aerial columns. 
It is assumed that the tube is capable of 
vibrating so that its particles move in planes 
perpendicular to the axis, with the same mo- 
tion in all directions from the axis, in the 
same transverse section. Then, if the vibra- 
tions of the tube be of very small extent, and 
