COMMON THINGS PUMPS. 



necessary purity, have been among the earliest mechanical and 

 physical inventions in every country. Natural springs showed 

 that sources of water existed in the lower strata of the earth. 

 This suggested the process of well-sinking or boring for water. 

 But the water when thus found rarely rises to the surface spon- 

 taneously. It does so in those deep springs called artesian 

 wells ; but in all ordinary cases where a shaft has been sunk 

 deep enough to find water, the water collects in the bottom 

 of the shaft, and never rises above a certain level. Expedients 

 are therefore necessary in all such case? to raise it to the 

 surface. 



2. The first and rudest of these contrivances, is to let down a 

 bucket by means of a rope, and thus to draw up one bucket-full 

 after another. The rope by which the bucket is elevated, when 

 the well is not very deep, is sometimes attached to the long ar:n 

 of a lever (fig. 1) the shorter arm being pulled down when 

 the bucket is drawn up full. This is perhaps the rudest and 



Fig. 1. 



most inartificial of all contrivances for the elevation of the 

 water. A pulley established over the mouth of the well is one 

 degree more efficient. 



The bucket being let down and dipped in the water, is drawn 

 up by pulling the rope. 



In this case the labour is expended not only in raising the 

 weight of the water and of the bucket which contains it, but also 

 that of the rope, which, if the well be deep, is not inconsiderable. 

 Besides this a certain force must be exerted to bend the rope con- 

 tinually over the groove of the pulley, and to overcome the 

 friction of the pulley itself in moving upon its axle. 



3. A windlass established over the mouth of the well (fig. 2) is 

 one degree, and only one degree, more efficient than these rude 

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