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POPULAR SCIENCE REVIEW. 
effected by tbe introduction of higli-pressurc steam worked 
expansively, we may conclude this part of the subject by 
observing, that we are far from arriving at that point of economy 
in the nse of steam which an increased pressure and a still 
greater expansion is calculated to attain. It is true that the 
danger of explosion may be increased, and so it would with 
our present means ; but in our locomotive engines we already 
work steam at 2001b. pressure on the square inch with greater 
safety than is done in our stationary engines at a reduced 
pressure ; it is, therefore, evident that we are behind in this 
department, and a wide field is still open for improvement. 
It is not our province in this article to point out how this can 
be accomplished, but we may safely affirm that the improvements 
already attained are only the precursors of others of much 
greater importance in the economy and use of steam. 
Marine Engines . — In this department of constructive art this 
country stands pre-eminently forward in advance of all others 
at the Exhibition. It is not the principle nor yet the power 
that attracts notice, but the application, design, and construc- 
tion of a machine calculated to propel a vessel of 6,000 tons 
burden, at a rate of from fourteen to fifteen knots an hour, and 
yet so small and so compact, compared with the magnitude of 
its force, as to excite the admiration of every beholder. In this 
department of mechanical science we have, concentrated within 
a space little more than twenty feet square, a force equiva- 
lent to 2,600 indicated horses'" power, and that with all the 
conveniences of approach to every part of these powerful 
machines. 
For examples of engines of these colossal dimensions and com- 
pact form, we have only to refer the reader to those of Penn, 
Maudsley, Eennie, Humphries, and others, to convince him of 
the superiority of their construction, the mathematical accuracy 
with which they are designed, and the precision with which 
they have been manufactured. In these respects they are 
superior to anything before accomplished in this country. 
Several specimens of a different kind have been exhibited from 
Prance and other parts of the Continent ; but they are not the 
best examples of the industry of those countries, excepting some 
small engines from Sweden, and a beautiful double-acting engine 
for river boats, by Messrs. Escher & Co., of Zurich. As a whole, 
the marine department has been well represented by engines of 
great power, and working models (chiefly by Maudsley & Field) 
of great beauty. 
If our limited space permitted, we might have gone more 
into detail, showing the various contrivances of the working 
parts ; under the circumstances, we must confine ourselves to 
the following outlines of the different types of marine engines, 
