applied in propelling Vessels in Navigation. 99 
round the perimeter of the wheel, about twenty-five degrees be- 
low the axle: two parallel openings will then remain at the 
lower part of the case, equal in depth to one-third the diameter 
of the wheel. Let each plane he one-third the diameter in 
depth, which size will leave the central part of the wheel to re- 
tain a considerable open space, according to the present general 
structure of steam-boat wheels. Let the machinery, thus formed, 
be lowered into water till the wheel becomes wholly covered with 
the fluid; and in that state, through a tube which has been pre- 
pared for the occasion, let air be forced into the machine till 
the water becomes depressed twenty-five degrees below the axle, 
when it will just meet the top of the lowest plane*. If the wheel 
be then made to revolve, the water will be drawn and extruded 
through the parallel openings at the bottom of the case, and 
the machine will be moved from its position by the resistance of 
the fluid to the acting planes. The condensed air by its speci- 
fic levity will always occupy the upper sections of the case, 
and by its elastie pressure will keep down the inclosed water 
very nearly to one determined horizontal level. Passing through 
the open space round the axle, the air by its fluent and springy 
properties will continue to arrange itself in the upper sections, 
conformably to any motion of the wheel, and im such a manner 
that its elastic pressure shall act almost equally on either surface 
of the upper planes, without producing a sensible obstruction to 
their movement. 
The machinery can easily be applied to any part of a boat or 
vessel; but it is calculated to ascertain if a central station can 
be practically occupied by a wheel. 
To prevent the escape of the condensed air through the groove 
in which the working end of the axle revolves, one method shall 
be described. Let a box, two feet long and two inches deep, 
by means of circular holes in the sides, be forced upon the end 
of the axle at the exterior of the machine, to which it must’ be 
closely attached. Let the box be nearly filled with water or oil, 
and let the condensed air, from the interior of the machine, be 
admitted through a fixed communicating tube, into the box 
above the fluid. The air, which endeavours to escape round the 
axle by its own elastic power, will then be resisted by the same 
power acting upon the fluid in the external box, and by the ad- 
ditional weight of the fluid also: therefore the air can never 
escape in that direction, unless the more dense fluid be first ex- 
* Our correspondent is probably not aware that the idea of inclosing 
the wheel in an air-tight case, and depressing the surface of the water 
hy means of injected air, was some years ago embraced in a poe ob- 
tained by Mr. Treyethick alone, or in conjunction with Mr. Dickinson. 
pelled 
