94 KANSAS UNIVERSITY (.)UARTERI,V. 



Many improvements have been made in windmills in the last few 

 years, and we hear rumors ot other and greater improvements to 

 be made in the near future. Doubtless engineers and inventors 

 have made many experiments on windmills, but they have not pub- 

 lished their results. It is surprising how few accurate data there 

 are in regard to the actual working of windmills — motors that are 

 in such general use and have been for centuries. There are really 

 none with the exception of a table in Engineering Magazine. Vol. 

 VIII, giving some results of measurements by Lieut. I. N. Lewis. 



The measurements of power made by the writer can not be con- 

 sidered comparative tests. The mills were not working under the 

 same conditions; some were heavily loaded, others lightly; still the 

 mills tested were in good working order: the exposure was good in 

 each case, the lift, quantity of water and wind velocity were care- 

 fully measured. The temperature and barometer pressure, though 

 not measured each time, -were found with suf^ficient accuracy for the 

 purpose. The experiments show the work each mill was doing 

 under its own conditions, not the work it might be made to do. 



Let ABED, Fig. 2, represent one slat or fan of a windmill, (' 

 the axis, R,, and R,, the radii or distances from the axis to the 



G 



Fig. 2 



ends of the fan, b,, and b,, tlu- eiul widtlis of fan. Let c be the 

 velocity of the wind, v the velocity of the wheel and Vj the rela- 

 tive velocity of the wind: that is, the velocity with respect to the 

 moving fan. Let .\ be the angle which the fan makes with the 

 direction of the wind, or axis C; )• the angle which Vj makes with 

 axis C. Let ^s be an}' small element of area of fan having a 

 length AR and width b,: r the heaviness of air, K a coefficient 

 whose value depends on curvature and friction of air on fan, L' 

 the power of the fan, and L the power of mill.. 



Fig. 3 shows /\s which we assume for simplicity to be a plane. 



The wind pressure /\P on /\^s, Fig. 3, is perpendicular to the sur- 

 face if we neglect the friction of air over the surface. This pressure 



