SCIENTIFIC SUMMARY. 
207 
records on a revolving plate the motion of the valve, and from the diagram 
so obtained the action of the valve can be studied, and any improvements 
in the arrangement of the gear can be at once imitated and tried. The 
instrument has been described and illustrated in “ Engineering.” 
Navigable Balloon . — The trials of M. Dupuy de Lome’s balloon at Paris 
have been of great interest, and appear to have been attended with an 
amount of success which is encouraging. The balloon is of an elongated 
form, so that it has a horizontal axis of least resistance, which is maintained 
parallel to the propelling force. The car has a huge rudder, consisting of 
a triangular sail of an area of 161 sq. feet. In order that this rudder may 
act, it is essential that the balloon should not drift with the wind, but 
should be propelled at a sensible velocity relatively to it. To effect this a 
large screw propeller of two blades is employed, 30 feet diameter, and 26 
feet pitch. This screw is rotated by four or eight men. According to 
M. Dupuy de Lome’s calculations, the resistance of the balloon at five miles 
an hour is 24 lbs., and at that speed the propeller should revolve twenty-one 
times per minute, four men having power sufficient to work the screw at 
that speed. The balloon, inflated with hydrogen, has a gross ascensional 
force of 3J to 3f tons. The total weight of the balloon and apparatus is 
If tons, and of the crew, stores, &c. 1J tons. In the experimental trial it 
was found that, with the screw working, the balloon did obey the rudder. 
It was found possible to direct the balloon at an angle of 12° with the wind’s 
direction. 
Flow of Elastic Fluids . — A valuable series of experimental researches on 
the efflux of air from orifices and its flow through tubes has been carried 
out by Mr. G. Wilson, and the results are being published in a Engineering.” 
Steel Gun. — Mr. Vavasseur, of the London Ordnance Works, is construct- 
ing a 12-inch built up steel gun, intended to prove the advantages of that 
system of construction by competing with any other gun of the same calibre. 
The rifling is a modification of the Lynal Thomas system, the gun being 
ribbed and the shot grooved. The gun is intended for a 110 lbs. charge of 
powder with 600 lbs. shot. 
Binary Vapour Engines . — Some of our readers may remember that between 
1850-60, M. Prospere Vincent du Tremblay constructed some engines, in 
which steam, in condensing, vaporised ether, the ether vapour being used to 
work a secondary engine. The object of the arrangement was to economise 
fuel, and the system of binary vapour engines was worked out by M. Trem- 
blay with great ingenuity, knowledge and thoroughness. The engines con- 
structed on this plan were fairly successful, and realised fair results as to 
economy of fuel, considering the date of the experiments. But the system 
was ultimately abandoned, in consequence of some difficulties with the 
joints, and from the danger of conflagration if there were any leakage of 
ether. Mr. J. H. Ellis, of Boston, has recently revived the system of binary 
vapour engines, using vapour of bisulphide of carbon in the secondary 
engine. The exhaust steam is led into a 11 vaporiser ” constructed some- 
what like a surface condenser, except that instead of being surrounded by 
cooling water the tubes are immersed in liquid bisulphide of carbon. The 
exhaust steam parts with its heat to this liquid vapourising part of it at a 
pressure of 40 to 60 lbs. per sq. inch. The vapour thus generated drives a 
