Hydrostatics. 37 



ton, which is higher than any of the places where 

 the pipes terminate. 



It is surprising that the antients should have 

 been totally ignorant of so simple a principle as 

 that of water rising to its level ; yet it is to this 

 ignorance that we owe those stupendous works 

 of art, the antient aqueducts, the ruins of which 

 we still behold with admiration. Thus, for in- 

 stance, in Plate V. fig. 19 5 an arch or arches 

 would have been built to carry the water from 

 the spring head at the side , across the valley, 

 to supply the house on the other side; whereas a 

 simple pipe of lead, iron, or wood, carried under 

 ground across the valley, will answer every pur- 

 pose, and supply the house and ponds about it 

 as amply as if an aqueduct had been constructed 

 on the antient plan. 



The reason why water thus rises to its level, 

 is because fluids press equally on all sides : thus 

 (in fig. 7.) if the tube B were taken away, the 

 water would still press at b with equal force as 

 before; and if the tube C were taken away, the 

 water would press against the part a as forcibly 

 as it would if it had remained. Thus, if with 

 the thumb we stop the end of the crooked tube 

 b (fig. 8.) at a, when full of water, the water 

 will press against the thumb with a force pro- 

 portioned to the height of the water in the tube 

 above a; and, if we remove the thumb, it will 

 run over at a, and fall in b to the level of a. 



To explain this in a popular way, without the 



