186 REPORT—1857. 
On the Construction of the 36-inch Mortars made by order of Her Majesty's 
Government. By R. MALLET. 
The author gave a verbal account of the two 36-inch wrought-iron mortars, and of 
the 36-inch shells constructed from his designs for the British Government. He 
described the peculiarities of their construction, to avoid difficulties of manufacture 
and of transport in service; and contrasted the powers of demolition as against forti- 
fied places, of these large shells, or transferable mines, with the 13-inch shell, the 
largest heretofore in use, concluding with some remarks on the application of wrought 
iron to artillery. 
On Tangent-Wheels. By GuitpForp L. MoLesworru. 
The author first presented some general views in hydraulics, and compared the 
efficiency of water-wheels, turbines and tangent-wheels. He then described and 
showed diagrams of a small wheel somewhat similar to the tangent-wheel, for a small 
workshop. 
A description was then given of a tangent-wheel sent by the author to Tasmania 
for driving a corn-mill of six pairs of stones, with the dressing machinery. The fall 
was 270 feet, with an available quantity of 2} cubic feet of water per second. The 
water was confined in a pipe and brought down to act on the periphery of a wheel 
3 feet in diameter, which revolved at a velocity of 360 revolutions per minute; the 
rims of the wheel were turned up truly on the shaft, and the edges of the inlet care- 
fully faced to correspond with them; the buckets were of wrought iron, cast into the 
rims, curved and ventilated ; the conditions to be observed in forming the curve of 
the buckets were described as requiring the water to enter without shock, remaining 
in the bucket sufficiently long to expend its vis viva, and then leaving it without dimi- 
nishing the effect ; the formation of these curves being the most important feature in 
producing an efficient machine. 
The toe of the shaft was so arranged as not to be submerged, and the oiling was 
managed by a convenient apparatus. 
The mechanical effect of the tangent-wheel was stated to be from seventy-five to 
eighty per cent., which was rather higher than that of Fourneyron’s turbine. 
Some experimenters had affirmed that Fourneyron’s turbines had given out as much 
as eighty-five or ninety per cent., but it was evident that such statements must arise 
from some mistake ; the consumption of power from different causes was stated to be 
about twenty-five per cent., leaving only seventy-five per cent. available ; the probable 
source of error was supposed to have arisen from the use of incorrect coefficients for 
efflux in gauging the amount of water passing through the turbine and probably in 
some instances from neglecting the element of velocity in the body of water gauged. 
Castel’s formula of Q=3:5 LH “H-+-035 2 was given as applicable to the case. 
It was also stated, that in practice Whitelaw’s turbines gave much less mechanical 
effect than that usually attributed to them, viz. seventy-five per cent. ‘The causes of 
loss of power were enumerated, and it was said that many which had been erected on 
the Continent had given great dissatisfaction, and had been for the most part replaced 
either by water-wheels, tangent-wheels, or turbines of a different kind. The tangent- 
wheel had, on the contrary, replaced well-constructed over-shot wheels, and had been 
highly approved of. 
The advantages of the tangent-wheel were summed up as follows :—Ist. The water 
deviated less from its course and was less broken up than in turbines. 2ndly. The 
tangent-wheel was capable of such regulation as to work with varying quantities of 
water with undiminished effect, one quarter of the maximum quantity of water pro- 
ducing as good a proportional effect as the maximum. 3rdly. It was cheap and — 
simple, and required no expensive foundations. 4thly. The toe of the shaft was not 
submerged in the tail-water. Sthly. The working parts were easily got at, and the 
. 
; 
pio s4 
wheel taken out in a few minutes for examination or repair. 6thly. The velocity of 
the wheel was not dependent on the quantity of water. 7thly. The motion was 
extremely steady and regular. 
The method of placing the wheel with its axis horizontal was stated to have been + 
tried, but without success, owing to the difficulty of freeing it of water. 
> 
Vcd 
Fs 
