116 
POPULAE SCIENCE EEVIEW. 
reach a maximum velocity, in some cases, o£ four feet a second, and which 
may he supposed capable of removing all the sediment carried or blown 
in. So also the large evaporation from the surface of the Bitter Lakes 
and Lake Timsah will cause an influx of water from both seas into the 
canal ; and the outflow from Lake Menzaleh can, if necessary, be directed 
into it, at its northern extremity. Mr. Hawkshaw has also calculated the 
probable rate of deposition of sediment from water flowing in, and the 
probable shallowing from air-borne sand, from which data he estimates 
that the cost of maintaining the canal by dredging could not exceed 
.£15,000 annually. After careful investigation, he attributes little weight 
to the objection raised on the supposed eastward drift of Nile deposit. 
Experiments on Armour-Plates . — We have noticed from time to time 
the experiments at Shoeburyness on the resistance of iron plates to pro- 
jectiles. It may now be assumed that the laws of resistance to the impact 
of projectiles at high velocities are approximately determined, and the 
most suitable qualities of the iron plates ascertained. There remain 
various questions as to the most suitable mode of supporting the armour 
casing, so as to offer the greatest resistance to shot, and at the same time 
to preserve the strength and sea-going properties of the vessel unimpaired. 
In July, experiments were made on a target constructed on the plans of 
Mr. George Clark, in which the armour-plates are attached by dove-tailed 
slots and bolt-bars to a backing of wrought-iron webs, forming a cellular 
system, the spaces of which are filled by pitch pine, teak, or millboard. 
This target resisted, with partial success, the blows of shot from the 
68-pounder smooth bore and 110-pounder rifled Armstrong guns, but 
succumbed to the 300-pounder projectiles fired with charges of 50 lb. and 
35 lb. of powder. These last smashed clear through 5|-inch armour- 
plate, backing, and inner skin. 
The Iron Plate Committee have reported that armour-plates should 
be bent, for ship-building purposes, at a bright red heat ; thus, for the 
present, settling a question on which there has been wide divergence of 
opinion. So treated, with precautions which they point out, the quality 
of the iron will, in their opinion, be improved rather than deteriorated. 
Destructive Effects of Projectiles . — Sir William Armstrong stated, in 
his address to the British Association for the Advancement of Science, at 
Newcastle, that, in conjunction with Captain Noble, he was prosecuting 
experiments to determine the waste of energy due to the disruption of 
the shot, by observing the increase of temperature of the fragments after 
impact. The mechanical force imparted to the shot by the ignition of the 
powder is reconverted into heat when its motion is arrested by impact, 
and this heat is divided between the object struck and the shot. By 
calculating from its velocity the work stored in the shot on leaving the 
gun, and ascertaining by Joule’s equivalent the wmrk remaining in the 
fragments of the shot as heat, the proportion taking effect on the shot 
instead of the armour-plate can be determined. The experiments showed 
an enormous absorption of power, caused by the yielding nature of the 
materials of which projectiles are usually formed. As we before pointed 
out, the superior efficacy of steel over cast-iron shot is due to the less 
proportion of work thus wasted. 
