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POPULAR SCIENCE REVIEW. 
second engine, and is then led into a coil of piping which is wetted by a 
shower of water and cooled by an air blast. It yet remains to be seen 
whether any economy can be attained by this plan sufficient to counter- 
balance the disadvantage of complication in the engine and the danger in 
using so inflammable a compound as bisulphide of carbon. 
Flexure of Iron and Steel. — M. Tresca has made some new experiments 
on the flexure of iron and steel railway bars, extending the experiments 
beyond the ordinarily assumed limit of elasticity. The loads were imposed 
by an hydraulic press, and the deflection at three points measured with 
great accuracy. Within the limit of elasticity, these experiments confirm 
the theoretical laws as to the proportionality of the deflections to the loads, 
and to show them to be inversely as the cube of the span. Beyond the 
stress ordinarily assumed as marking the limit of perfect elasticity, they 
show that the imposition of more and more energetic loads causes the limit 
of elasticity to be extended, so that by repeatedly loading the bar it may 
approach the point of rupture. The bar takes increasing permanent curva- 
ture, but its temporary deflections remain proportional to the loads. The 
original co-efficient of elasticity diminishes to an extent which may amount 
to one-tenth part. 
MEDICAL SCIENCE. 
Determination of the Mode of Flight in Birds. — M. Marey, who has in- 
vestigated this subject very extensively, adds to his researches a note in the 
11 Comptes Rendus ” [February 26th, 1872], He has already shown that the 
wing of the bird describes an ellipse. He states that the graphic traces 
which have enabled him to come to this conclusion have also allowed him to 
determine the height of the wing at each moment, consequently he has 
been able to determine the velocity with which either the elevation or 
depression of the wing is affected. But he says that to determine the work 
done by the bird, to ascertain the resistance which is opposed by the air each 
moment to the movements of elevation or depression of the wing, it is 
necessary also to know the angle at which this organ strikes the air. The 
resistance, it seems, varies enormously in the case of a bird’s wing, accord- 
ing as the motion takes place parallel or perpendicular to its plane. This 
question is then, with the aid of diagrams, pursued by the author. We 
believe, too, that a very interesting paper on this subject has been published 
by Dr. J. Bell Pettigrew. We have not seen the paper itself, but the u Edin- 
burgh Medical Journal ” for February contains an extremely favourable 
notice of it. 
How the Nerves end. — Dr. Lionel Beale, F.R.S., has had a paper on this 
subject in the 11 Monthly Microscopical Journal ” for January, 1872, in which 
he endeavours to forward his opinion of the termination and distribution of 
nerve-fibre. This was apropos of a controversy which has taken place 
between him and Dr. Klein, who we believe has a paper on the subject of 
nerves, which will appear in the a Monthly Microscopical Journal ” for April. 
Dr. Beale states that Dr. Klein showed him some drawings of the termina- 
tion of the nerve-fibres, but he adds , <( His specimens were prepared by the 
