112 FERGUSON'S LECTURES. 



extremity of one sail, to that of the opposite one, each being six 

 feet and a half in width, is capable of raising 926 pounds, two 

 hundred and thirty-two feet in a minute ; and of working on an 

 average eight hours per day. This is equivalent to the work of 

 thirty-four men : twenty-five square feet of canvas performing the 

 average work of a day-labourer. A mill of this magnitude sel- 

 dom requires the attention of more than two men ; and it will 

 thus be seen, that making allowance for its irregularity, wind 

 possesses a decided superiority over every species of animal 



labour. The advantages arising from the use of steam as a 



prime mover in machinery will be examined in a subsequent 

 page 



