, 



HYDROSTATICS. 



rior be so much less than that of the ex- 

 terior air, as to allow for the weight of 

 the materials as a counterpoise, the bal- 

 loon cannot be made to float even in a 

 stationary manner; but when liberated 

 will fall to the ground. The contents of 

 . the balloon being ascertained in cubic 

 feet, it will be easy to ascertain what 

 weight the balloon can lift, when filled 

 with rarified air, according as that may 

 have been rendered more light than the 

 atmospheric air: if filled with gas, the 

 interior will be at least seven times light- 

 er than an equal quantity of atmospheric 

 air. From this it will be seen, that to 

 bear up a weight of 300$. the balloon 

 must be large, and the specific gravity of 

 its contents be adequate to overcome the 

 resistance of that impediment. As the 

 air of the upper part of our atmosphere 

 becomes gradually more rare, and conse- 

 quently lighter, according to its distance 

 from the earth's surface, we may con- 

 clude that there is a point in its altitude, 

 beyond which a balloon could not soar ; 

 because its own weight, even if nothing 

 were appended, would at such a point 

 perfectly equipoise the difference be- 

 tween the confined gas and the surround- 

 ing atmosphere. And this is the more 

 perfectly to be admitted, from the know- 

 ledge we have acquired of the difficulty 

 with which balloons are made to reach 

 certain heights, and of their ascent being 

 shown (by the slower fall of the mercury 

 within the barometer) to be far^ slower 

 in the upper regions when they approach 

 that state of equipoise. Were it not for 

 the opposition offered by the superior 

 air, a balloon would rise instantaneously, 

 from the moment of its liberation, in a 

 most rapid manner, to that height where 

 its equipose should be found. We have 

 said thus much in explanation of the na- 

 ture of the balloon, as appertainingto the 

 laws of hydrostatics, referring the reader 

 to the article AEROSTATION, for whatever 

 appertains to the practical experience we 

 have had of that science, which at first 

 seemed to promise the most important 

 aid to vr.rious others, but in which it has 

 completely failed : the whole of the prin-, 

 ciples on which aerostation depends have 

 been long understood. 



We shall now speak of the diving-bell, 

 which also depends on hydrostatic prin- 

 ciples, though, like the balloon, it has a 

 close connection with pneumatics. The 

 upper part of a diving-bell is always made 

 to contain a certain quantity of air, more 

 or less compressed, in proportion to the 

 depth to which the bell sinks. Thus, if 



we invert a small 'tumbler into a vessel 

 nearly filled with water, and allow it to 

 descend perpendicularly, so that no air 

 may be allowed to escape, the water will 

 rise a very little way within it. If the 

 tumbler be but partially immersed, the 

 water could at the utmost but rise to its 

 own level; but if immersed so deep as to 

 exceed its own interior, and thatjthe bot- 

 tom edge of the tumbler does not touch 

 the bottom of the vessel, the water will, 

 in consequence of its own greater weight 

 at a greater depth, rise rather, though 

 scarce perceptibly, higher in the tum- 

 bler, and occasion the air to be compress-' 

 ed into a smaller space. But the quantity 

 of vital principle in the compressed air 

 will be equal to that quantity of air in the 

 open atmosphere which would fill the in- 

 terior of the tumbler. If the inverted 

 tumbler were first placed at the bottom 

 of an empty vessel, and that water were 

 afterwards poured into the latter, the ef- 

 fect would be precisely the same. 



The air contained within the upper 

 part of a diving-bell not only debars the 

 ingress of water, but, like the rarified air 

 in the balloon, gives the machine such a 

 buoyancy, that, unless made very substan- 

 tial, and duly laden at the bottom, or 

 broadest part, it would sink with difficul- 

 ty, and be apt to turn on its side, so that 

 the air would escape. Under the head of 

 DfvraG-6e#,' the reader will find an ample 

 detail of the inventions hitherto extant in 

 that branch of adventure. 



With regard to the depth to which float- 

 ing bodies, become immersed in fluids, 

 we may consider the following general 

 principles, or propositions, to be suffi- 

 cient for the purpose of our readers. 

 Bodies, whose bases, or bottoms, are an- 

 gular, like the keels of ships, will be 

 immersed deeper than those whose bases 

 are flat, such as barges : hence sharp- 

 built vessels necessarily (to use the tech- 

 nical term) "draw Jmore water" than 

 those of a more obtuse form : the reason 

 of which is easily demonstrated, viz. As 

 every body floating on a fluid will-be ira-^ 

 mersed in proportion to its weight, anil 

 will displace a quantity of water equal 

 thereto, it follows, that as a triangle is 

 equal to only half a parallelogram of equal 

 base and altitude, a parallelogram (or flat- 

 bottomed vessel) will, under equal pres- 

 sure, sink only half the depth of a triangu- 

 lar shaped bottom, of equal base and alti- 

 tude. For the same reason, vessels that 

 have sharp stems make an easier passage 

 though the water than such as are more 

 "bluff," or obtuse, " at the bows:" the 



