308 FARM MOTORS 



should be well placed, not too close in, so that as the 

 wheel is thrown out of the wind there is not too much 

 jar. Rubber should never be used for this spring, as the 

 continual use and exposure to the weather will cause it 

 to harden or flatten so that it is of no use. Generally 

 weights are better to hold the wheel in the wind than 

 springs. 



In support of back or forward geared mills there is not 

 much more to say than has been said about direct con- 

 nected. The most vital parts of these mills other than 

 named above are the gearings. They must be well set 

 and well designed so that when they wear there is not 

 a very great chance for them to slip. 



430. Power of windmills. Probably there is no other 

 prime mover which has so many variables depending 

 upon it as the windmill, when we undertake to compute 

 the power by mathematical means. It is also hard to 

 distinguish between the greatest and the least of these 

 variables, so the author gives them promiscuously. Vari- 

 able velocity of wind ; velocity greater on one side of 

 wheel than on the other ; angle of weather of the sails ; 

 thickness of sails; width of sails; number of sails; length 

 of sails ; obstruction of tower either behind or in front 

 of wheel ; diameter of wheel ; velocity of sails ; variation 

 of load, and location and height of tower. In all the tests 

 of windmills which have been carefully and completely 

 carried out it is shown that as the wind velocity increases 

 or decreases the load should increase or decrease accord- 

 ingly; as the velocity of the wheels increases, the angle 

 of weather should decrease, and vice versa. Wide sails 

 give more power and a greater efficiency than narrow 

 sails. 



A. R. Wolff gives the following table as results for 

 wood-wheel mills: 



