THE WORK OF AIR AND WATER 



this opinion questionable." It has been supposed 

 by other writers that windmills were used in France in 

 the sixth century, while still others have maintained 

 that this mechanism was unknown in Europe until 

 the time of the Crusades. All that is tolerably certain 

 is that in the twelfth century windmills were in use in 

 France and England. It is recorded that when they 

 began to be somewhat common Pope Celestine III. 

 determined that the tithes of them belonged to the clergy. 



INHERENT DEFECTS OF THE WINDMILL 



The mediaeval European windmill was supplied 

 with great sails of cloth, and its picturesque appear- 

 ance has been made familiar to everyone through the 

 famous tale of Don Quixote. The modern windmill, 

 acting on precisely the same principle, is a comparatively 

 small affair, comprising many vanes of metal, and 

 constituting a far more practical machine. The great 

 defect of all windmills, however, is found in the fact 

 that of necessity they furnish such variable power, 

 since the force of the wind is incessantly changing. 

 Worst of all, there may be protracted periods of atmos- 

 pheric calm, during which, of course, the windmill 

 ceases to have any utility whatever. This uneradicable 

 defect relegates the windmill to a subordinate place 

 among prime movers, yet on the other hand, its cheap- 

 ness insures its employment for a long time to come, 

 and the industry of manufacturing windmills continues 

 to be an important one, particularly in the United 

 States. 



[69] 



