342 Review of Allen’s Mechanics. 
300°, the air is not rendered unpleasant for respiration. On this ac- 
count steam pipes produce a temperature at once mild and agree- 
able.”—p. 97. 
The consideration of heat concludes with some valuable remarks 
and suggestions on the structure of flues of chimnies, stovepipes, and 
different kinds of stoves, which all persons will take more or less in- 
terest in reading. 
Thus far the book relates to matter, as forming the compound parts 
of machines, or as subject to their action, and to the effects of the 
principal natural agents or powers upon material substances. The 
subjects next treated upon, and which may more appropriately than 
the foregoing, be termed mechanics, are 1. Power, whether derived 
from wind, water, steam or animals, with rules for calculating the 
same.—2. Motion, under which several interesting topics are dis- 
cussed.—3. Mechanical powers, as defined and explained in other 
elementary works.—4. Hydrodynamics, which includes among other 
things, pressure of fluid substances,—hydrostatic press, which is one 
of the most simple and beautiful machines for producing vast mechan- 
ical effects by means of a fluid, and illustrates most perfectly the ax- 
iom that what is gained in power is lost in velocity,—aqueducts, wa~ 
ter level, levelling instruments, rules for levelling, floating power of 
fluids, hydrometer, rules for calculating the pressure of fluids upon 
the bottom and sides of vessels and upon flood-gates, embankments, 
pipes, &c. and for proving their strength ; most of which subjects 
are to be found in elementary works on mechanics, but are ex i 
here in a manner adapted to the comprehension of common readers. 
—5. Hydraulics —6. Water wheels, under which heads, the mill 
wright, engineer, and all persons concerned in the management of 
water power, will find a rich fund of information, elementary and 
_ practical, and in which the author has furnished more suggestions from 
his own experience and observations, made in this country and: in 
urope, than in other parts of the book. If these were duly ob- 
served, we should not so often hear of miscalculations in the power 
of mill streams, the construction of dams, embankments, trenches, 
and in the structure of different kinds of water wheels, that have 
many instances within our knowledge, been attended with great loss 
of property to the owners. A description is here given of the value 
of reservoirs of water connected with ponds, with calculations and 
directions for forming them; a subject rarely to be found in treatises 
of the kind. There are two or three minor things omitte 
