Revievi of Allen's Mechanics. 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 efiects 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 

 litde 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 ordinary 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 



" 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, accompa- 

 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 at a 

 temperature which will not have the disagreeable effect upon the air 

 abovementioned. Whenever the heat of a stove does not exceed 



