362 PHILOSOPHICAL TRANSACTIONS. [aNNO ITSQ. 



than would be required, if the cloth was increased on the same radius. The 

 itiost useful figure therefore for practice, is that of N° Q or 10, as has been ex- 

 perienced on several mills in large. 



Table IV. Contuhiing the Result of 6 Sets of Experiments, made for deter- 

 mining the Difference of Effect j according to the Different Felocity of the wind. 



JV, JB. The sails were of the same size and kind as those of No. 10, II, 12, Tab. IV, Continuance 



of the experiment one minute. 



//. Concerning the Ratio between the f^elocity of IVindmill Sails Unloaded, and 

 their Felocity when Loaded to a Maximum. 



Those ratios, as they turned out in experiments on different kinds of sails, 

 and with different inclinations, the velocity of the wind being the same, are 

 contained in column 10 of tab. 3, where the extremes differ from the ratio of 

 10 : 7.7 to that of 10 : 5.8 ; but the most general ratio of the whole will be 

 nearly as 3 : 2. This ratio also agrees sufficiently near with experiments where, 

 the velocity of the wind was different, as in those contained in tab. 4, col. 1 3, 

 in which the ratios differ from 10 : 6.9 to that of 10 : 5.9. However, it ap- 

 pears in general, that where the power is greater, whether by an enlargement 

 of surface, or a greater velocity of the wind, that the 2d term of the ratio is 

 less. 

 III. Concerning the Ratio between the Greatest Load that the Sails will bear 



without Stopping, or, what is nearly the same thing, between the Least Load 



that ivill Stop the sails, and the Load at the Maximum. 



Those ratios for different kinds of sails and inclinations, are collected in col. 

 11, tab. 3, where the extremes differ from the ratio of 10 : 6 to that of 10 : 9.2 ; 

 but taking in those sets of experiments only, where the sails respectively an- 



