THK(1KKI'1CAI, AND MKASUREU I'U.Ml'INO I'OWF.R OK WIN' 1 )M I M.S. 



103 



of wind velocity and the corresponding number of strokes of the 

 pump may be in error quite a little; but the mean of a good many 

 such measurements cannot be far from correct. In each figure we 

 have drawn a line AB to represent the mean, or so as to have, at 

 every stroke, about as many circles above as below it. 



For ordinar}^ pumping velocities, that is, from 8 to 14 miles per 

 hour, this line is straight. It represents the relation between wind 



Fiff. 8.— 10 ft. steel mill. :iT ft. -lbs. per stroke. Fig. 10.— 6 ft steel mill, 34..5 ft.-lhs. 



per stroke. 



vilocity and number of strokes of pump; but since the number of 

 strokes is proportional to the power of the mill, it follows that this 

 line represents the relation between velocity of wind and power of 

 milk 



Here we note a difference between theory and measurement. 

 From equation ( 12 ) or (13 ) it is seen that for any given mill the 

 theoretical relation between power and wind velocity is an equa- 

 tion of the third degree — a cubic parabola, while from an\' of the 



«r lY; rs' sCo 



Fig. 9.-23 ft. wood mill. 156.T ft. -lbs. per stroke. 



figures it is seen that for velocities from 8 to 14 miles per hour this 

 relation is an equation of the first degree — a straight line. 



