HYDROSTATICS. 



Intermitting Springs- Those springs which flow and stop by regular 

 aternations may be accounted for upon the principle of the syphon, represented 

 at fig. 17. If this tube be filled with water, and the shorter leg be plunged into 

 a vessel of water, the water will flow up the tube, over the bend, and out at the 

 longer leg, till the vessel is emptied. 



Fig. 18 represents a section of a hill, having within a cavity, A, from which 

 runs a channel in the form of a syphon ; the rain falling upon the hill, preco- 

 lates through the crevices and pores, d d d, and in course of time will fill the 

 cavity with water up to the level, E E ; it will then flow over the bend, B, and 

 continue to flow and supply the spring till the level of the water falls below the 

 mouth of the channel, when the action of the syphon will cease, until, by fresh 

 supplies, the level of the water is again raised, so as to flow over the bend, when 

 the syphon will act as before. 



The Hydrostatic Press- Fig. 19. This is perhaps the most powerful 

 machine ever invented, the only assignable limits to its power being the strength 

 of the materials of which it is formed. A is the force pump, by the action of 

 which water is forced through the small tube, B B, and its pressure communicated 

 to the mass of water in the cylinder, c, there the water in its endeavour to resist 

 compression forces up the moveable piston, D D, with its burden, and the action 

 of the pump being continued, the pressure is gradually increased until the 

 required degree is produced. 



Fluid Support Specific Gravity- A solid body immersed in a fluid 

 displaces exactly its own bulk of fluid, and the force with which the body is 

 buoyed up, is equal to the weight of the fluid which is displaced ; therefore, the 

 body will sink or swim, according as its own weight is greater or less than the 

 bulk of the displaced fluid. This refers to bodies of less density than water. 

 Any body of greater density than water, when wholly immersed in that fluid, 

 loses exactly as much of its weight as the weight of an equal bulk of the water 

 which it displaces. 



These laws are of much importance, as an acquaintance with them enables us 

 to explain innumerable phenomena in nature, in reference to the floating of bodies 

 in water, or in the atmosphere. 



Fig. 20 is a vessel of water, and A a solid body of the same density im- 

 mersed in it, and which, being equally pressed upon from above and below, 

 retains its position, just as the mass of water it has displaced would have done. 

 But if a solid body as B, fig. 21, heavier than water, bulk for bulk, be placed in 

 it, it will sink to the bottom ; while a body lighter than water will float on the 

 surface partially immersed, as A, fig. 21, the weight of the water displaced 

 being equal to the weight of the whole solid. Thus, the weight of any floating 

 body may be ascertained by measuring the quantity of water which it displaces. 



F'ig. 22 represents the hydrostatic balance used for ascertaining the specific 

 gravity of solid bodies, which are suspended in water by a horse-hair attached 

 to the bottom of the scales. 



Hydrometers- These are instruments which, beittg immersed in liquids, 

 determine the proportion of their densities, or specific gravities, and thence their 

 qualities. The use of the hydrometer depends on the following propositions : 

 1. The hydrometer will sink in different fluids in an inverse proportion to the 

 density of the fluids. 2. The weight required to sink a hydrometer equally 

 far in different fluids will be directly as the fluids. Each of these two proposi- 

 tions gives rise to a particular kind of hydrometer; the first with the graduated 

 scale, as fig. 23, the second with weights, usually hollow glass beads of various 

 weights, which are dropped into the liquid till one is found to remain stationary, 

 indicating t8e density of the liquid. 



Fig. 24, represents Nicholson's hydrometer, consisting of a hollow copper ball 

 A, with a steel stem B, supporting a small dish c. By the successive addition of 

 weights to the dish c, the instrument may be sunk so as to obtain the complete 

 range of specific gravity. 



Fig. 25, represents the areometer, an instrument for determining the relative 

 specific gravities of any two fluids which may be poured together without mixing, 

 as mercury and water, oil and water, &c. 



