ON THE GENERAL DIFFUSION OF KNOWLEDGE. 



and makes them lighter and more agile, than if 

 they were constructed of solid matter. In like 

 manner the bones of birds, which are thinner 

 than those of other animals, and the quills in 

 their wings, acquire by their thinness the 

 strength which is necessary, while they are so 

 light as to give sufficient buoyancy to the ani 

 mal in its flight through the aerial regions. Our 

 engineers and carpenters have, of late, begun to 

 imitate nature in this respect, and now make 

 their axles and other parts of machinery hollow, 

 which both saves a portion of materials and ren 

 ders them stronger than if they were solid.* 



The departments of hydrostatics and hydrau 

 lics, which treat of the pressure and motion of 

 fluids, and the method of estimating their velo 

 city and force, require to be thoroughly under 

 stood by all those who are employed in the 

 construction of common and forcing-pumps, 

 water-mills, fountains, fire-engines, hydrostati- 

 cal presses , and in the formation of canals, wet- 

 docks, and directing the course of rivers ; other 

 wise they will constantly be liable to commit 

 egregious blunders, and can never rise to emi 

 nence in their respective professions. Such 

 principles as the following : that fluids press 

 equally in all directions, that they press as 

 much upwards as downwards, that water, in 

 several tubes that communicate with each other, 

 will stand at the same height, in all of them, 

 whether they be small or great, perpendicular or 

 oblique, that the pressure of fluids is directly 

 as their perpendicular height, without any regard 

 to their quantity, and that the quantities of 

 water discharged at the same time, by different 

 apertures, under the same heigth of surface in 

 the reservoir, are to each other nearly as the 

 areas of their apertures, will be found capable 

 of extensive application to plumbers, engineers, 

 pump-makers, and all who are employed in 

 conducting water over hills or vallies, or in 

 using it as a mechanical power, by a recogni 

 tion of which they will be enabled to foresee, 

 with certainty, the results to be exnected from 

 their plans and operations ; for want of which 

 knowledge many plausible schemes have been 

 frustrated, and sums of money expended to no 

 purpose. 



The following figures and explanations will tend 

 to illustrate some of the principles now stated : 

 1 . Fluids press in proportion to their perpen 

 dicular heights, and the base of the vessel con 

 taining them, without regard to the quantity. 

 Thus, if the vessel ABC, fig. 2, has its base 

 BC equal to the base FG of the cylindrical ves- 

 s&amp;lt; i DEFG, fig. l,but is much smaller at the top 

 A than at the bottom, and of the same height ; 

 the pressure upon the bottom BC is as great as 



* The mechanical reader who wishes particular 

 information ou this subject is referred to the article 

 &rf.n&amp;lt;rth of materials in Enty. Brit- 3d edit, which 

 was written by the late Professor Robison. 



the pressure upon the bottom of the vessel DE 

 FG, when they are filled with water, or any 

 other liquid, notwithstanding that there will be a 

 much greater quantity of water in the cylindri 

 cal than in the conical vessel ; or, in oihf r words, 

 the bottom BC will sustain a pressure equal to 

 what it would be if the vessel were as wide at 

 the top as at the bottom. In like manner, the 

 bottom of the vessel HIKL, fig. 3, sustains a 

 pressure only equal to the column whose base if 

 KL, and height KM, and not as the whoie 

 quantity of fluid contained in the vessel ; all the 

 rest of the fluid being supported by the sides. 

 The demonstration of these positions would oc 

 cupy too much room, and to many readers would 

 appear too abstract and uninteresting; but they 

 will be found satisfactorily demonstrated in most 

 books which treat of the doctrines of hydros- 

 tatics. 



2. The positions now stated form the founda- 



