114 
POPULAR SCIENCE REVIEW. 
of the British Association at Birmingham. According to Mr. Thomson’s 
statement, in all previous rotary engines a steam stop or abutment is necessary, 
and in this lies the fatal objection to their employment. The steam stop 
must get out of the way of the revolving piston at each rotation, and from 
its necessarily rapid motion, imposes mechanical difficulties of the most in- 
. superable character. In Mr. Thomson’s engine these are avoided, by dispensing 
with the abutment altogether : two pistons are used, which have an alternately 
accelerated and retarded motion, concentrically with the cy finder, and the 
retarded piston acts, for the time being, as the abutment to the accelerated 
piston. The engine has no valves, nor eccentric gear of any kind ; it possesses 
peculiar facilities for reversing, and it may be worked at a fixed rate of ex- 
pansion as easily as with full steam. Its cost will not exceed half that of an 
ordinary engine. Gas exhausters, on the same principle, have been con- 
tracted and used with success. 
The Rouquarol Self-regulating Diving Apparatus . — A description has ap- 
peared in the Engineer of October 27, of the extremely ingenious diving appa- 
ratus of M. Rouquarol, which has been adopted in the French navy, and was 
exhibited to members of the English Admiralty during the international 
courtesies at Cherbourg. This apparatus renders the quantity and pressure 
of the air supplied to the diver quite independent of the pressure and quantity 
-supplied by the pumps, being, in fact, regulated by the lungs of the diver 
himself ; and in one form of the apparatus he is independent of the pumps 
altogether, carrying a reservoir of air on 
his back, with a supply sufficient for half 
an hour’s work under water. The ordinary 
cumbrous helmet and air-tight dress is en- 
tirely dispensed with. 
Fig. 1. shows the regulator of the air in 
section, r is a reservoir of compressed air. 
Above this reservoir is the equilibrium or 
air-case, b. This case is closed at its upper 
part by means of a metallic or wooden plate 
of a lesser diameter than the casing, and 
Skeleton Diagram of the Regulator, connected to it by a sheet of india rubber 
or other flexible material. It is obvious, therefore, that the air in the 
chamber b must always be of the same pressure as the environment of the 
diver, adjusting itself to that pressure by the rising or falling of the metallic 
plate on its flexible hinge. The reservoir r and the air-chamber b communicate 
by a small hole closed by a conical valve, c, opening downwards. This conical 
valve is connected to the metallic cover of the equilibrium chamber, so 
that as that cover descends it opens the conical valve and admits the com- 
pressed air from the reservoir r, which, in turn, raises the cover and closes 
the valve, t is the inhaling-tube ; m, the mouth-piece ; and s, a valve, 
through which the exhaled air is expelled. The mouth-piece is placed between 
the teeth of the diver, his nose being closed by spring nippers. The reservoir, 
in communication or not with the pumps, is placed on his back, and loaded 
weights on his feet ; and, thus prepared, he is enabled to dive to any depth, 
Breathing the air as securely as above the surface of the water. At each 
inspiration, the cover of the air-chamber falls, and opens for an instant the 
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b 
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