YEA 



When the sail is in motion, and of course near the extremities of the 

 sail, when it moves faster, tha angle of weather must be less. 



Maclaurin makes the weather to vary from 260 34', at the point of the 

 sail nearest the centre, to 9 at its extremity. Mr Smeaton, however, 

 by experiment has found the following angles to answer as well as any- 

 The radius is supposed to be divided into six parts, and ^th reckoning 

 from the centre is called 1, the extremity being denoted 6. 



Angle with Angle with the 



No. the axis. plane of motion. 



1 72 18 



2 71 19 



3 72 18 middle. 



4 74 16 



5 77| 12| 



6 83 7 extremity. 



4. From Smeaton 's experiments it appears, that a windmill works to 

 the greatest advantage, when it is so constructed that the velocity of 

 the sails is to their velocity when they go round without any load, as a 

 number between 6 and 7 is to 10 ; and also that the load, when the mill 

 works in this manner, is to the load that would just keep it from mov- 

 ing, nearly as 8,5 to 10. 



5. With different velocities of wind the load that gives the maximum 

 effect varies nearly as the square of the velocity, and the effect itself as 

 the cube. 



WIRE, time of sun's passing. See Time. 



Y 



YEAR, length of. 'See Earth element! of, and Calendar, 



353 



