SCIENTIFIC SUMMARY. 
99 
through either the forward or aft nozzles, or through one forward and one 
aft nozzle at pleasure. The delivering nozzles are of brass, 2 feet 1 inch 
by 1 foot 7 inches or about 452 square inches sectional area. 
The engine has three cylinders 38i- inches diameter and 3 feet 6 inches 
stroke. 
The following results were obtained on the trial, the draught being 9 feet 
9 inches and the lower edges of the jet nozzles being 8 inches below the 
water level. 
First run. A half knot tide against the ship ; speed, 8*276 knots; revo- 
lutions of engines, 41 ; steam pressure, 24 lbs ; vacuum, 26 inches. 
Second run. A half knot tide in the ship’s favour ; speed 9*549 knots; 
revolutions of engines, 42 ; steam pressure, 25 lbs ; vacuum, 26 inches. 
Mean spead = 8*912 knots. 
It will thus be seen that the u Waterwitch ” attained a speed sensibly 
identical with that of the a Viper,” a twin screw, armour-plated gunboat of 
precisely similar tonnage, displacement, and engine power. Still the per- 
formance of the “ Viper ” compared with that of other vessels can hardly 
be considered satisfactory, and the most that can at present be assumed 
is that the new system of propulsion is capable of attaining results equal to 
the less satisfactory results with the ordinary screw propeller. 
The Rev. J. A. L. Airey, M.A., has mathematically investigated the 
theoretical conditions of the action of the jet. His calculations show that 
only 18*82 per cent, of the indicated horses’ power is usefully applied in the 
propulsion of the vessel; 18*33 per cent, is wasted in the residuary velocity 
of the water ; and another 10 per cent, is probably consumed in engine fric- 
tion, leaving 52*85 per cent, still unaccounted for. 
Our own opinion is that a large part of the want of success is due to the 
inefficiency of the centrifugal pump, which was not of the best, type, and 
might be most materially improved by a more scientific disposition of the 
vanes, and by the addition of Professor Thomson’s whirlpool chamber. 
Steel Bridge. — A bridge of the inverted bowstring form, constructed of 
puddled steel, has been erected by Major Adelskold at the Gotha Elf, in 
Sweden. . The span is 137^ feet, and the total weight of the structure is only 
50 tons. The maximum strain on the material is calculated at 8 tons per 
square inch, and all the parts of the bridge were teste#?o 16 tons per square 
inch. 
Channel Bridge. — In addition to the tunnel schemes for carrying a railway 
across the English Channel, Mr. McClean is reported to have proposed a 
bridge. 
Institute of Mechanical Engineers. — At the last meeting of this Society at 
Birmingham, a paper was read by Mr. John Robinson on Seller’s self-adjust- 
ing Injector for feeding boilers, a most valuable improvement on the Gifiard 
Injector, which is now so extensively used, making it automatic with a 
varying steam pressure. Also a paper by Mr. E. W. Webb on a curvilinear 
shaping machine, for finishing the curved inner face of locomotive wheels to 
a true circle. 
Crumlin Viaduct. — This beautiful example of the Warren or triangular 
girder, which had become dangerous from the loosening of the joints, con- 
sequent on an insufficiency of bearing-area, has been thoroughly renovated, 
YOL. YI. — NO. XXII. I 
