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XLVII. On the Immersion of a small Spherical Ball in a Jet 
of high-pressure Steam. By A CORRESPONDENT. 
[ ‘a paper which appeared in the last (January) Number 
of this Magazine, Mr, Armstrong makes us acquainted 
with the curious circumstance, that when a small spherical 
ball is hung by a thread in a jet of high-pressure steam a 
sensible force is required to draw it out: I shall endeavour 
shortly to account for this pheznomenon. 
The most obvious explanation which presents itself is, that 
the lateral pressure of the steam is greater nearer the side of 
the jet than it is internally, but as the pressure at the surface 
can only be equal to the atmospheric pressure, this method of 
explanation seems to be attended with some difficulty ; never- 
theless there can be little doubt it is the true one. 
Suppose we have a vertical tube inserted in the steam-boiler 
haying a piston capable of moving within it. When the 
piston is allowed to yield to the pressure of the steam, it will 
move along the tube until it either remains at rest or retro- 
grades, 
Let E represent the pressure of the steam on the piston 
at any instant, e the atmospheric pressure in a state of rest; 
then if we consider the pressure of the air on the external 
surface of the piston not sensibly to vary from the atmospheric 
pressure, the piston will be urged along by a variable force 
Ee. It is perfectly clear that when the piston ceases to move 
forwards the force Ke must have changed its sign, or the elastic 
force of the steam on the surface of the piston must be then 
less than the atmospheric pressure. The above proceeds on 
the supposition that the atmospheric pressure on the external 
surface of the piston does not sensibly vary during the motion: 
but in the case supposed this could not possibly be true. 
Nevertheless, if instead of a fixed tube with a piston moving 
in it we had a moveable tube with its external aperture closed 
and sliding in an orifice in the boiler, the extra atmospheric 
force called into play by the motion would be less than in the 
former case; and this nearly approximates to what must 
happen in the central part of the jet of steam when it is al- 
lowed to escape with perfect freedom from the boiler. Now 
it is impossible to estimate this extra force of resistance called 
into play by the motion, which will of course depend upon | 
the velocity, and that according to a law of which we have no 
knowledge. Yet it is perfectly conceivable that the law of 
resistance may be such, as that in the first instance the actual 
force of resistance should be less than the elastic force of the 
steam in the jet. ‘Che consequence of this would be, that the 
