NEW INVENTION OF A BLAST WHEEL. 
107 
ifs diameter small, compared with its 
length, the following are the principal ma- 
thematical results respecting the motion of 
the air, so far as it is consequent upon the 
vibrations of the tube. 
1. The motion of the particles situated on 
the axis wilt take place in the direction of the 
axis, and will be nearly the same as if an im- 
pulse were originally given in this dii'ection, 
and the propagation were rectilinear. 
2. At all points of the same transverse sec- 
tion, the motion, estimated in a direction pa- 
rallel to the axis, will be nearly the same. 
3. If the tube be made to vibrate isochro- 
nously, and so as to contain, at equal interya's 
a'ongits length, nodal sections and sections 
of maximum vibration, it wall produce in the 
fluid vibrations of the same duration, with 
points of quiescence and of maximum vibra- 
tion at intervals corresponding to vibrations 
of that duration in air. 
4. But unless the nodal sections of the tube 
be fixed, the duration of these simultaneous vi- 
brations will not be permanent till the intervals 
between the nodal sections become the same 
in the tube as in the column of air : and then 
a nodal section of the tube is nearly coinci- 
dent with a section of maximum vibration of 
the fluid. 
From these results it follows that there are 
certain transverse vibrations of the tube which 
will impress on the fluid column the same 
kind of motion as it is known can be given to 
it by vibrations excited near one extremity of 
the tube, when the other is onen. Mathemati- 
cians have succeeded in satisfactorily repre- 
senting the circumstances of the motion in the 
latter case of disturbance, by assuming, from 
experiment, that the open end is a position of 
maximum vibration, or nearly so ; but hitherto 
no distinct cause for this fact has been assign- 
ed Mr. Challis thinks it may be shown mathe- 
matically, that the aerial vibrations, ex- 
cited at the extremity of the tube, and 
propagated along its interior, will put it 
into the state of vibration, wliicli, as appears 
from the foregoing results, will produce an 
effect the same in kind as that observed. 
But to what decree the phenomenon may be 
attributed to this cause, can be learnt only 
from experiment; by ascertaining whether 
the vibrations of the tube have any consider- 
able influence on the intensity of the musical 
sounds. The following fact seems to favour 
the idea of a sensible influence. A sound 
produced under glass (for instance, the tick- 
ing of a French clock under a glass covering), 
is louder than when the glass is removed, 
plainly by reason of the internal reflections 
and the propagation of the vibrations along its 
surface, which cause it to vibrate so as to act 
with increased effect on the external air. It 
is not easy to discern that the glass vibrates, 
but the increase of sound is proved to be 
owing to this cause, when, on pressing the 
glass with the palms of the hands, the inten- 
sity is diminished. This experiment may sug- 
gest the means of detecting the influence of 
the vibration of a solid, in other instances of 
a similar nnime.— Proceedings of the British 
Association: Land, and Edinb. Phil. Mag,, 
xml. vii., p. 300. 
HYDRAULIC BLAST-WHEEL, 
In founderies, smitliles, and other manufac° 
tories, large quantities of atmospheric air in 
rapid motion are in constant demand, and a 
jarge proportion of the motive power is spent 
in the supniy. The pressure of fluids being 
equal in all directions, the aggregate amount 
of force employed in transmitting air by means 
of bellows, air-cylinders with pistons, &;c., is 
very considerable, there being the same pres- 
sure on every square inch of the blowing- 
apparatus, as on the like space of the orifice 
through which the air is transmitted. 
The accompanying drawings represent a 
blast-wheel lately invented by me, of which 
the following is a description. I have had a 
model of it made, and it fully verifies the cor- 
rectness of my calculations ; and in this case 
the effects must be the same in proportion on 
a large scale. 
Fig. 1. A is a hollow cylinder (the length 
of twice its diameter), which is made to re- 
volve on the pivots O by means of a rope or 
belt acting on the pulley B, or by any other 
mechanical power. C is a stationary nose or 
tube, fixed to the side of the oval trough D. 
'Phe trough is nearly full of water, its level 
being above the centre of the cylinder A, and 
of the small cylinder within it, hereafter de- 
scribed. Within the cylinder A is a spiral 
leaf wound round a cylinder of about 1th of 
the diameter of the external one. The size 
of the internal cylinder need not be increased 
in proportion to that of the external. The 
leaf is soldered to both cylinders, and so ren- 
dered air-tight; it may be made of the slight- 
est material. 
Fig. 2. The water is here seen occupying 
the lower half of the cylinder and trough, the 
top being always filled with air. On the 
wheel’s making one revolution, the water in 
E is conveyed into F ; that which was before 
in F escapes at G, and flows round the sides 
and bottom of the trough, outside the cylinder, 
to re-enter the latter at H. The air in I 
(which is continually supplied by atmospheric 
pressure of 15 lbs, to the square inch) is con- 
veyed to K,and so in proportion for less than 
a revolution ; and the air which was before in 
K is forced through the pipe at C, to which 
branch-pipes may be attached. A continuous 
blast of air is thus produced, and may be con- 
veyed to any part of a building, The pre.?sur 0 
