^ ^VIND-MILLS. 223 



Now we have already seen, when treating of " appU- 

 cation of labor," that a horse traveling three miles an 

 hour for eight hours, will overcome only 83 lbs. with 

 ordinary working, which is not double the resistance 

 of the wind. Hence we perceive that more than half 

 the horse's strength is lost by driving against such a 

 current. At six miles an hour, all his strength, with- 

 out over-driving, would be expended in overcoming 

 the force of the wind, and the power required for mov- 

 ing the carriage would be so much excessive labor. 

 For simplifying the operation, the increased motion of 

 the wind occasioned by driving against it has not been 

 taken into account. 



Even with a small pressure, the loss in power is con- 

 siderable for an entire day. When, for example, the 

 air is perfectly still, travehng six miles an hour will 

 cause a constant resistance of 3 lbs. on the carriage, or 

 one fourteenth of the power exerted for a full day's 

 work. The same speed against a " gentle wind" of six 

 miles an hour, added, would increase the resistance four- 

 fold, or equal to 12 lbs. ; more than one fourth of the 

 horse's strength at six miles an hour through the day. 



^VIND-MILLS. 



The power possessed by the sails of a wind-mill 

 may be nearly ascertained in the same way, the area 

 of the sails being known, and first deducting their av- 

 erage velocity. 



The force of wind may be usefully applied by al- 

 most every farmer, as it is a universal agent, possess- 

 ing in this respect great advantages over water-power, 

 of which very few farms enjoy the privilege. 



