A HISTORY OF 



water, converted into steam, has been found 

 capable of raising a weight of twenty tons ; 

 and would have raised twenty thousand, were 

 the vessel confining it sufficiently strong, and 

 the fire below increased in proportion. 



From this easy yielding of its parts to ex- 

 ternal pressure, arises the art of determining 

 the specific gravity of bodies by plunging 

 them in water ; with many other useful dis- 

 coveries in that part of natural philosophy, 

 called hydrostatics. The laws of this science, 

 which Archimedes began, and Pascal, Avith 

 some other of the moderns, have much im- 

 proved, rather belongs to experimental than 

 to natural history. However, I will take leave 

 to mention some of the most striking paradox- 

 es in this branch of science, which are as well 

 confirmed by experiment, as rendered uni- 

 versal by theory. It would, indeed, be un- 

 pardonable, while discoursing on the proper- 

 ties of water, to omitgiving some account of the 

 manner in which it sustains such immense 

 bulks as we see floating upon its soft and 

 yielding surface : how some bodies, that are 

 known to sink at one time, swim with ease, if 

 their surface be enlarged: how the heaviest 

 body, even gold itself, may be made to swim 

 upon water; and how the lightest, such as 

 cork, shall remain sunk at the bottom : how 

 the pouring in of a single quart of water, will 

 burst a hogshead hooped with iron : and how 

 it ascends, in pipes, from the valley, to travel 

 over the mountain : these are circumstances 

 that are at first surprising ; but, upon a slight 

 consideration, lose their wonder. 



" In order to conceive the manner in which 

 all these wonders are effected, we must be- 

 gin by observing that water is possessed of 

 an invariable property, which has not hither- 

 to been mentioned ; that of always keeping 

 its surface level and even. Winds, indeed, may 

 raise it into waves, or art spurt it up in foun- 

 tains ; but ever, when left to itself, it sinks in- 

 to a smooth even surface, of which no one 

 part is higher than another. If I should pour 

 vrater, for instance, into the arm of a pipe of 

 the shape of the letter U, the fluid would rise 

 in the other arm just to the same height; be- 



In the above sketch, the manner of demonstrating 

 used by Monsieur D'Alembert is made use of, as the most 

 obvious, and the most satisfactory. Vide Essai sur, &c. 



cause, otherwise, it would not find its level, 

 which it invariably maintains. A pipe bend- 

 ing from one hill down into the valley, and 

 rising by another, may be considered as a 

 tube of this kind, in which the water, sinking 

 in one arm, rises" to maintain its level in the 

 other. Upon this principle all water-pipes 

 depend; which can never raise the water 

 higher than the fountain from which they 

 proceed. 



Again, let us suppose for a moment, that 

 the arms of the pipe already mentioned, may 

 be made long or short at pleasure ; and let 

 us still further suppose, that there is some ob- 

 stacle at the bottom of it, which prevents the 

 water poured into one arm, from rising in the 

 other. Now it is evident, that this obstacle 

 at the bottom will sustain a pressure from the 

 water in one arm, equal to what would make 

 it rise in the other; and this pressure will be 

 great, in proportion as the arm filled with wa- 

 ter is tall. We may, therefore, generally con- 

 clude, that the bottom of every vessel is pres- 

 sed by a force, in proportion to the height of 

 the water in that vessel. For instance, if the 

 vessel filled with water be forty feet high, the 

 bottom of that vessel will sustain such a pres- 

 sure as would raise the same water forty feet 

 high, which is very great. From hence we 

 see how extremely apt our pipes, that con- 

 vey water to the city, are to burst ; for de- 

 scending from a hill of more than forty feet 

 high, they are pressed by the water contained 

 in them, with a force equal to what would 

 raise it to more than forty feet high ; and that 

 this is sometimes able to burst a \vooden pipe, 

 we can have no room to doubt of. 



Still recurring to our pipe, let us suppose 

 one of its arms ten times as thick as the other; 

 this will produce no effect whatsoever upon 

 the obstacle below, w r hich we supposed hin- 

 dering its rise in the other arm ; because, how 

 thick soever the pipe may be, its contents 

 would only rise to its own level; and it will, 

 therefore, press the obstacle with a force 

 equal thereto. We may, therefore, univer- 

 sally conclude, that the bottom of any vessel 

 is pressed by its water, not as it is broad or 

 narrow, but in proportion as it is high. Thus 

 the water contained in a vessel not thicker 

 than my finger, presses its bottom as forcibly 

 as the water contained in an hogshead of an 



