250 



MACHINERY IN CONNECTION WITH AIR. 



ri;];. 270. 



"Wind-mills, like the preceding, which have fixed sails, 

 should not he more than three or four feet in diameter, 

 and even then will require care in storms. If larger, 

 they will become broken by severe winds. The remedy is 

 either to move the sails by hand at every considerable 

 change in the force of the current, which would require 

 hearly constant attention ; or to use the self-regulating ma- 

 chines, of which there have been several invented, some 

 of which have proved useful and durable. 



SaUidaxfs wind-mill has been much used for several 

 years, and is made of various sizes, the larger possessing 

 the power of several horses. It is self-regulated, in the 

 following manner : "When the mill begins to run too fiist, 

 it pumps water rapidly into a chamber or cylinder, and 

 this increase of water moves an arm which turns the fans 



