SCIENTIFIC SUMMARY. 
113 
very remarkable amount of negative slip of the screw, the velocity due to 
the pitch of the screw being only 12 knots. The screw propeller used in 
these trials was a novel modification of the Mangin screw, having no less 
than eight blades, in four pairs. It is probable that when this propeller is 
replaced by one more in accordance with ordinary practice, the discrepancies 
between the estimated and actual speed will partly disappear, and the per- 
formance of the vessel w 7 ill correspondingly improve. 
British Association for the Advancement of Science. — Amongst the more 
interesting papers read before the mechanical section of the Association at 
Birmingham, we may refer to the history of the development of the Bessemer 
process, by Mr. Henry Bessemer ; a paper on chain-cable-testing machinery, 
by Sir William Armstrong ; Mr. Levick’s paper on coal-cutting machinery ; 
Mr. Cowper’s description of the lock-saw-gin for cleaning cotton ; and Mr. 
Bobinson’s account of the Giffard injector. In reference to ' this last, the 
most novel facts were, that the steam-jet pump had been applied in combina- 
tion with the injector in cases where the level of the supply-water was much 
below that of the injector itself, the water having been raised by suction, in 
some cases to a height of 16 feet by this means ; and that a simple form of 
the injector had been applied to raising water in mines. In one remarkable 
case, with steam pressure of 45 lbs. per square inch, corresponding to a column 
of water of only 104 feet, the water was actually raised to a height of 261 feet 
vertical. 
Machinery for Puddling Iron. — The increasing difficulties caused by the 
disputes between masters and men in Staffordshire are causing attention to 
be redirected to the possibility of puddling iron by machinery, and more 
than one system of machine puddling is undergoing thorough trial and in 
vestigation. At the Dowlais works, Mr. Walker’s plans are being tried 
with encouraging results, the molten metal being brought into contact with 
the flame by the rotation and oscillation of the vessel containing it, the 
process being completed by the ordinary hand labour. Mr. Bennett, of the 
Wombridge Works, Salop, has introduced another system, in which the 
ordinary rabble, or rake, is worked at the rate of 50 strokes per minute, 
mechanism outside the furnace. With single furnaces and charges of 5 cwt., 
the consumption of coal is 28 cwt. per ton of puddle bar made. With 
double furnaces and 10 cwt. charges, the consumption of coal is only 17 cwt., 
being a reduction of 39 per cent. M. Gaudray has described to the Insti- 
tute of Civil Engineers of France, a similar system in use at St. Dizier. 
The rabble receives from machinery attached to the brickwork of the furnace 
a rectilinear motion transverse to the furnace, and at the same time a slower 
travelling motion lengthways of the furnace, by which it is brought succes- 
sively over every part of the furnace floor. The saving in fuel is shown by 
the following figures 
Before the machine was applied ... 15*21 cwt. coal per ton pig iron. 
With the machine 11*79 „ „ „ 
Machine thrown out of action ... 13*43 „ „ „ 
The balling up of the iron is effected by hand labour in the ordinary way. 
j Rotatory Engine. — An extremely interesting and ingenious form of rotary 
steam engine was exhibited by Mr. B. W. Thomson, C.E., at the meeting 
YOL. Y. — NO. XVII I. I 
