118 
POPULAE SCIENCE EEVIEW. 
brittle, the qualities so induced being easily destroyed, and the original duc- 
tility and malleability being restored by annealing at a high temperature. 
The drift of Mr. Treadwell’s argument is to show that in the condition of 
hammer hardness the iron is best fitted for use in strengthening cast-iron 
guns, its extension under strain being then in closer relation with the exten- 
sion of the cast-iron core. In his experiments he employed wire of i^ch 
diameter, and the most important conclusions from these are as foDow : — 
First, that with iron hardened by tension and compression, in the condition 
of hard wire, the amomit of permanent elongation, under tension, is far 
smaller than the permanent elasticity up to near the breaking-point, and 
also that the permanent elongation does not begin until about one half the 
breaking strain is ap]3lied. Second, that when the material has been sub- 
jected to a strain’ of a given amount, the repeated application of a strain 
within that amount produces no further permanent elongation. Third, that 
when the iron is annealed, the permanent elongation commences at a com- 
paratively low strain, and its extent is large in proportion to the elasticity of 
the iron. Hence, when annealed iron is applied on a cast-iron gun, it must 
be loosened, or suffer the cast-iron to break within its grasp before a strain 
on it up to half its tensile strength has been reached. 
Comparing two guns of a calibre of 14 inches. Professor Treadwell estimates 
the ultimate resistance of one with annealed iron hoops at 540,344 lb. for 
each inch in length of the reinforce of the gun, and of one with hammer- 
hardened hoops at 1,199,800 lb. per inch, or more than twice as much. 
“ Royal Sovereign ^ — This vessel, now fitted with Captain Coles’s cupolas, 
has made a successful cruise, the turrets proving perfectly manageable in 
the roughest water, with the vessel rolling through an arc of 21°. 
Atmospheric Hammer. — A practical mechanic at Birmingham, Mr. Grim- 
shaw, has invented an atmospheric hammer on the same principle as the 
famous steam hammer of Mr. Nasmyth, but actuated by air compressed by 
an air-pump driven by an ordinary belt and pulley. The air is compressed 
into a reservoir forming the framework of the machine, and serving as an 
“ accumulator ” of power. 
Armour Plates. — The Iron Plate Committee has closed its labours by some- 
experiments on a target designed by Professor W. Pole. This target repre- 
'sented the side of an iron-plated vessel, 17 feet long and 10 feet high, covered 
with plates 5ft. 9in. long, by 2ft. 6in. wide, §,nd varying in thickness from in. 
to 5-f4in. The backing consisted of vertical oak timbers, 11 inches thick,, 
outside planking of teak 10 inches, and inside planking of oak 6 inches thick. 
The armour plates were fastened in the French fashion, with fifteen 1|^ inch 
“wood screws” instead of bolts. The results of the experiment showed the 
immense advance which has been made in the manufacture of the plates, 
those on the target being as tough as could be desired ; they also proved the- 
great superiority of the French “wood-screws” to our own system of bolts,, 
the plates being held in their place in spite of the most terrific battermg ; 
whereas the bolts usually break, and allow the plates to buckle forwards, and 
ultimately fall off. The superiority of Captain Palliser’s chilled shot was 
again exhibited, and a cast-iron shot with a 35 lb. charge broke up harm- 
lessly against the target. Shot of 160 and 220 lb. weight, of cast steel, from 
Armstrong shunt guns, penetrated the target with the greatest ease, covering; 
