Review of Allen’s Mechamies. 341 
an. equilibrium between the weight and power.” Galileo too, ob- 
serves, “that what appears very firm and succeeds very well in mod- 
els, may be very weak and infirm, or may even fall to pieces by its 
own weight, when it comes to be executed in large dimensions, ac- 
cording to the model.” It must be obvious then to every one, that 
rules and directions for calculating the amount of friction and other 
impediments to motion with precision, must be all important to the 
machinist. 
_ The subject of heat occupies about fifty pages, upon which, the 
author has been at pains to consult the most approved works recently 
offered to the public, and has added the result of his own experience. , 
Here, as on other subjects, are given an elementary treatise, and then 
the effects of heat upon machinery, and in carrying on the useful 
arts, as distillation; and in generating steam for working engines, with 
rules and calculations of its power, and of the comparative value for 
this purpose, of different kinds of fuel. His remarks on the domes- 
tic'use of fuel, though somewhat of a departure from mechanics, are 
interesting to all persons. From the calculations exhibited, we learn, 
that Lehigh coal is actually cheaper, when used for heating rooms 
by means of close stoves, than English coal, by 150 per cent ;—that 
when R. Island coal costs five dollars fifty cents per ton, and Le- 
high eight dollars, the same quantity of heat may be obtained from the 
same cost of fuel; or that a ton of R. Island coal is actually worth a 
little less than three fourths of a ton of Lehigh coal. 
- From a table inserted page 96, it appears, that it costs ten times as 
much to heat rooms by means of ordmary open fire-places, as by 
close stoves with long pipes or funnels; and that an open parlour 
grate requires five times the expense for fuel, and an open Franklin 
stove nearly three times the expense, to produce an equal degree 
of heat to the air of an apartment. 
On the quality of the heat thus imparted he observes, that — i 
“The principal objection urged against the use of close stoves, is 
the confined dry air produced by them. It is well known. that air, 
which passes over iron or bricks heated red hot, acquires a disagreea- 
ble odor, and produces a harsh sensation upon the lungs, aecompa- 
nied-by a tendency to cough. The clay or fire bricks, with which 
anthracite coal-stoves are lined, being slow conductors of heat, are 
peculiarly well adapted for keeping the external part of the stove ata 
temperature which will not have the disagreeable effect upon the air 
abovementioned. Whenever the heat of a stove does not exceed - 
