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 

 ef 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. Hydi'odynamics, 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 explained 

 here in a manner adapted to the comprehension of common readers. 

 — 5. Hydraulics. — 6. Water ivheels, under which heads, tlie 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 

 Europe, than in other parts of the book. If these were duly ob- 

 served, we should not so often hear of miscalculations in tlie power 

 of mill streams, the construction of dams, embankments, trenches, 

 and in the structure of different kinds of water Avheels, that have in 

 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 omitted under 



