100 
POPULAR SCIENCE REVIEW. 
scarcely be said that the improvement is thoroughly sound in principle, and 
promises to be of much practical use. 
Experiments on Rigidity . — The rigidities of glass, brass, and steel have 
been very carefully determined by Dr. J. D. Everett, on a method suggested 
by Sir William Thomson. 
Steel, Strength of. — Mr. T. E. Vickers, of Sheffield, has made some interest- 
ing experiments on the strength of steel, the proportion of carbon being 
approximately determined at the same time. With 0-33 per cent, of carbon 
the tenacity was 30*4 tons per square inch, and the strength increased 
steadily as the amount of carbon became greater, until vsdth 1‘25 per cent, 
of carbon the tenacity reached 69 tons. Simultaneously the elongation of 
the bars diminished from 1*37 metres to 0’62 inches, and the specific gTavity 
from 7*871 to 7*823. The toughness, as indicated by capacity for resisting 
blows, was greater in the steels which contained least carbon. 
Concrete Buildings . — Some experiments are being made in Paris and at 
Gravesend in building houses with concrete walls, and an interesting paper 
on the subject will be found in a recent number of the Fortnightly Review, 
by Henry Conybeare, Esq., C.E., in which the opinion is expressed that con- 
crete walls, faced with glazed tiles, will form the most important element in 
the future of London architecture. 
Resistance to Projectiles . — Experiments by the Eev. F. Bashforth, under 
the direction of the Ordnance Select Committee, give for the resistance of 
the air to the motion of projectiles, 
p z=z (3 
or the resistance proportional to the cube of the velocity. 
Testing Iron hy Magnetism . — A method of ascertaining the existence of 
flaws in wrought-iron bars by the magnetic needle has been discovered by 
Mr. Saxby, and has for some time been under experiment at Chatham. The 
results of some of these experiments are described by Mr. Paget in the 
Engineer. If a bar of homogeneous soft iron be placed in the magnetic 
equatorial plane, that is, nearly east and west, it will become temporarily 
magnetic, one side of the bar assuming a north, and the other a south 
polarity. If, now, a small magnetic needle be passed in front of this bar, it 
will not be disturbed from its true position at right angles to the bar. If, 
however, the bar be not homogeneous, but composed of iron of different 
degrees of hardness, or containing flaws and solutions of continuity, the 
magnetic condition of the bar will no longer be uniform, and in passing in 
front of it, the small magnetic needle will deviate from its true position. In 
the recent experiments at Chatham, Mr. Saxby examined in this way a 
number of bars, and marked on them the points at which any deviation of 
the needle was observed. These bars were afterwards broken in the testing 
machine, and in every instance broke at the points marked by Mr. Saxby. 
A bar of three descriptions of iron, welded up and painted over, was shown 
to Mr. Saxby, who immediately detected the inequality of texture. A 
small pin of steel was inserted longitudinally into a 4-inch wrought-iron bar 
and welded up ; its position was accurately detected by the needle. No 
method has yet been found for testing plates. 
Endurance of Heavy Guns. — Mr. Arthur Bigg, C.E., has endeavoured to 
