119 



the sail with the plane of rotation increases towards the axis; 

 but it is not clear that he has any rule for determining those 

 angles, more than that they were the angles of those sails 

 with which he experimented, which produced the greatest 

 mechanical effect. The following are the angles which he 

 prescribes : — 



smeaton's construction. 



Radius divided into 6 equal parts, 

 Angle of the sail with the axis ... 



1 



2 



Mid- 

 dle, 



3 



4 



5 



Ex- 

 tremity 



6 



72 

 18 



71 



19 



72 

 18 



74 

 16 



774 



83 

 7 



CONSTRUCTION HEREBY RECOMMENDED. 



Weather angle, supposing the ex- 

 Ditto, supposing the middle 18°... 



37 

 43 



20J 

 26J 



14 

 18 



101 

 13f 



84 



11 



7 

 9 



With sails formed upon Smeaton's plan, I am not surprised 

 that he found the whole cylinder of wind could not be 

 advantageously intercepted ; but with properly constructed 

 sails, I am persuaded that he would have arrived at a differ- 

 ent conclusion, and that he would also have found, that the 

 angle at which the extremity of the sail might be advan- 

 tageously set, would admit of a much more extensive range, 

 where the products of the velocity, multiplied by the weight 

 raised in a given time, would have produced an uniform 

 maximum result. At least, so I have inferred from the 

 following experiments. 



It is not easy to show the unnecessary obstruction, and 

 consequent loss of power, which the wind encounters from 

 ill-formed sails; but if water be the medium in which the 

 sails are made to revolve, very conclusive evidence of the 

 fact may be exhibited. If in any vessel of water a number 

 of small pieces of paper, bran, or other light body of about 

 the same specific gravity as water be sprinkled, the effect 



