304 PHILOSOPHICAL TRANSACTIONS. [anNO 17 5g. 



Maxim 7. The load at a maximum that sails of a similar figure and position 

 will overcome, at a given distance from the centre of motion, will be as the 

 cube of the radius. 



Maxim 8. The effect of sails of similar figure and position, are as the square 

 of the radius. 



Carol. 1 . Hence it follows, that augmenting the length of the sail, without 

 augmenting the quantity of the cloth, does not increase the power ; because 

 what is gained by the length of the lever, is lost by the slowness of the rotation. 



Corol. 2. If sails be increased in length, the breadth remaining the same, the 

 effect will be as the radius. 



FI. Concerning the velocity of the Extremities of PVindmill Sails, in Respect to 



the Velocity of the fViyid. 



Maxim Q. The velocity of the extremities of Dutch sails, as well as of the 

 enlarged sails, in all their usual positions when unloaded, or even loaded to a 

 maximum, are considerably quicker than the velocity of the wind. 



The Dutch sails unloaded, as in tab. 3, No. 8, made 120 revolutions in 52" : 

 the diameter of the sails being 3 feet 6 inches, the velocity of their extremities 

 will be 25.4 feet in a second; but the velocity of the wind producing it being 6 

 feet in the same time, we shall have 6 : 25.4 :: l'.4.2\ in this case therefore, 

 the velocity of their extremities was 4.2 times greater than that of the wind. In 

 like manner, the relative velocity of the wind, to the extremities of the same 

 sails, when loaded to a maximum, making then QS turns in 52", will be found 

 to be as 1 : 3.3; or 3.3 times quicker than that of the wind. 



The following table contains 6 examples of Dutch sails, and 4 examples of the 

 enlarged sails, in different positions, but with the constant velocity of the wind 

 of 6 feet in a second, from table 3 : and also 6 examples of Dutch sails in dif- 

 ferent positions, with different velocities of the wind, from table 4. 



