IV 



THE WORK OF AIR AND WATER 



THE store of energy contained in the atmos- 

 phere and hi the waters of the globe is in- 

 exhaustible. Its amount is beyond all cal- 

 culation; or if it were vaguely calculated the figures 

 would be quite incomprehensible from their very 

 magnitude. It is not, however, an altogether simple 

 matter to make this energy available for the pur- 

 poses of useful work. We find that throughout 

 antiquity comparatively little use was made of either 

 wind or water in their application to machinery. 



Doubtless the earliest use of air as a motive power 

 was through the application of sails to boats. We 

 know that the Phoenicians used a simple form of sail, 

 and no doubt their example was followed by all the 

 maritime peoples of subsequent periods. But the use 

 of the sail even by the Phoenicians was as a compara- 

 tively unimportant accessory to the galaxies of oars, 

 which formed the chief motive power. The elabora- 

 tion of sails of various types, adequate in extent to 

 propel large ships, and capable of being adjusted so 

 as to take advantage of winds blowing from almost any 

 quarter, was a development of the Middle Ages. 



The possibilities of work with the aid of running 



[62] 



