454 RECAPITULATION. 



Wheel-Carriages. 



1. Wheels of carriages turn round, on account 

 of the friction they sustain in contact with the 

 roads. 



2. Large wheels, in general, are more advan- 

 tageous than small ones. 



8. In four-wheeled Carriages, the fore-wheels 

 are made smaller than the hind ones, for the con- 

 veniency of turning j otherwise they would be 

 better of the same size. 



4. Broad wheels are better for heavy carriages — 

 such as waggons — because they press and harden, 

 instead of cutting up the roads as small wheels do. 



ABSTRACT OF HYDROSTATICS. 



1. Hydrostatics treat of the mechanical proper- 

 ties of non-elastic fluids, such as water. 



2. The cause of fluidity is not perfectly known; 

 but it cannot be owing to any particular con- 

 figuration of particles, since fluids and solids are 

 convertible into each other by adding or substract- 

 ing heat. 



3. A portion of fluid gravitates in another, when 

 surrounded by a larger portion, in the same way 

 as if it were in the air. 



4. Fluids press in all directions equally. 



5. A fluid presses in proportion to its perpen- 

 dicular height, and the base of the vessel contain- 

 ing it, without any regard to the quantity. 



6. By specific gravities, is meant the relative 

 weights of equal bulks of different substances. 



