118 
POPULAR SCIENCE REVIEW. 
Trials in 1856 gave for the speed of the Shannon, with a common screw, 
10-49 and 11‘69 knots per hour, with 1,957 and 2,216 horses’ power 
respectively. In the recent experiments the common screw was again 
tried — first with the leading corners of the blades removed, and then with 
both corners cut away, so as to approximate their form to the blades of 
the Griffiths screw. The speed reduced in both cases. The Mangin 
screw gave a higher speed than the common screw, but caused so much 
vibration as to preclude its adoption in the English navy. As this appeared 
to arise from the locking of the water between the parallel blades, an 
ingenious modification was suggested with Mangin blades set at equi- 
distant intervals round a Griffiths boss. Screws of this form, with three, 
four, and six blades, were tried : the vibration entirely ceased in the two 
latter cases, and an increase of speed was gained as compared with the 
original Mangin. 
Common screw (one corner cut) 
Speed 
in Knots. 
11-29 ... 
Horses’ 
Power. 
2,055 
„ „ (both corners cut) .. 
11-08 ... 
2,094 
Mangin (with two pairs of parallel blades) ... 
11-33 ... 
2,034 
Three Mangin blades on boss 
11-49 ... 
— 
Four „ „ „ 
11-55 ... 
2,021 
11-24 ... 
1,947 
The experiments with the Griffiths screw have not yet been com- 
menced. 
The Black Prince attained in her trial trips a speed of 13"584 knots. 
The Warrior reached 14-354. These mail-clad vessels are so similar that 
the difference is not easily explained. Nevertheless, both are unap- 
proached by any similar vessels in the world, either in speed or power. 
The time-honoured process of riveting for structures of wrought-iron i 
is likely to be gradually superseded by a far more perfect process. In 
riveting, half the strength of the plate is lost in consequence of the metal 5 
punched out for the reception of the rivets. Mr. Bertram has contrived i 
a process which, after many difficulties, is coming into use, and has , 
been employed for parts of the mail-clad vessels now building. In this I 
process the edges of the plates are heated by the flame of two portable ,| 
coke furnaces and welded, so that no strength is lost. Wrought-iron 
structures thus constructed will be perfectly homogeneous and seamless. 
A cannon of aluminium bronze has been manufactured by Mr. 
Christophe, and presented to the French Government. The alloy is 
known to possess extraordinary toughness. 
The constantly-renewed discussion of boiler explosions has gradually led to 
a much better appreciation of their causes, and the theory of Mr. Colburn 
does not leave much to be desired. Corrosion at or near the water line is 
known frequently to occur to such an extent as to cause rupture at 
ordinary pressures; and this would afford an easy explanation of many i 
explosions, were it not that the boiler-shell is frequently torn to fragments 
and the surrounding buildings demolished in a degree more resembling 
the effects of springing a gunpowder-mine than the escape of steam at 
common pressures. Hence gradually-accumulated over-pressure has been 
