340 Review of Allen’s Mechanies. 
abandoned after a course of unsuccessful experiments, may be found 
collected as rubbish, forming a sort of museum of injudicious and 
abortive contrivances.” A book like the one before us, is calculated 
to prevent the waste of property in this manner, by pointing out the 
practical modes of success, and the common sources of failure. 
_ The first hundred pages are occupied with a consideration of mat- 
ter as acted upon or modified by certain natural powers, as gravita- 
tion, cohesion, magnetism, electricity, galvanism and heat, which ap- 
pear to have most important effects upon all solid bodies, producing 
ehanges in their gravity, strength, hardness, fluidity and forms. In 
discussing these subjects, the author keeps constantly in view the de- 
sign and object of his book, to wit, the application of science to the 
arts, in a manner adapted to the capacities of manufacturers and me- 
chanics, avoiding a pedantic display of technical terms and ostenta- 
tious speculations, too often to be found in works of this kind, and 
which embarrass the inquiries of those who are deficient in scientific 
edueation. After a brief explanation of gravitation, he gives tables 
and calculations for estimating the specific gravity of the substances 
manufactured or used in manufactories, with: directions for doing it 
by admeasurement, by which the weight of sheets of malleable and 
east iron, of copper and lead, also, of square or round bars, of 
ropes, and of iron and lead pipes, can be ascertained, without the 
use of a balance of any kind, and even while these articles make @ 
component part of machinery. After an explanation of cohesion, 
there is exhibited the comparative strength of materials to resist com- 
pression, or being crushed, as the stiffaess of beams, bars, &c. long!- 
tudinal strength to resist being pulled asunder in the direction of their 
lengths; as cables, chains and anchors, bars, &c.; also, power t0 
resist twisting or torsion, as gudgeons, journals of shafts, &c. with 
rules for calculating the strength of the same, and of wheels, revolv- 
ing shafts, and other parts of machinery. 
The next thirty pages treat of matter geometrically defined, and 
contain rules and calculations for determining the solid contents 
superficies of walls, timber and other like substances of every form. 
This is followed by numerous practical remarks on friction, and other 
kinds of resistance to motion, with rules for estimating their amount 
and influence upon various kinds of machinery.‘ From the resist 
ance of friction alone,” it has been observed by Mr. Fergusom 
‘“‘there are few compound machines that do not require a third part 
- more power to work them when loaded, than is sufficient to constitute 
