518 PHYSIOLOGY AT THE FARM. 



forward through 33,000,000 of feet (33,264,000) ; but that 

 number divided by 20 will give a product approaching to the 

 ordinary effort of a man in a day, or the raising one Ib. verti- 

 cally through little short of two millions of feet (1,663,200) ; 

 or, what is plainly the same thing in respect to dividend and 

 the product, the raising of one Ib. vertically through 33,000,000 

 feet and, when one- twentieth is taken, the raising of one Ib. 

 through nearly 1,600,000 feet.* In the second case, in which 

 the load is supposed to be 300 Ib., that and the weight of the 

 body, 150 Ib., make together 450 Ib. ; that weight carried 

 horizontally through one mile, or 5280 feet, equals one Ib. 

 carried similarly through 450 X 5280 = 2,376,000; so that, 

 to equal the performance in the first, the 300 Ib. load would 

 require to be carried just fourteen miles,-)- an effort probably 

 beyond the limit of human strength so that this case in- 

 dicates the kind of limits within which the rule adopted by 

 Professor Playfair is applicable. 



In taking as a standard of animal power the number of 

 pounds weight that can be raised to the height of one foot in a 

 day, it would be very desirable that the standard should require 

 no qualification as to the mode in which the animal power is 

 exerted ; but that in an absolute manner is impossible, chiefly 

 because velocity, or the rapidity with which the task is to be 

 accomplished, makes so great a difference on the requisite 

 muscular exertion. When the velocity does not make a mate- 

 rial element of the case, a near approximation to an absolute 

 standard seems attainable. Taking the mechanical effect of 

 walking on a level as equal to l-20th of the effort made in 

 raising the same weight vertically, the following statements 



* Weight of body, 150 Ib., load, 200 Ib. = 350 ; 350 x 5280 feet in a mile 

 3 miles an ho 

 t 33,264,000 



oo 



x 3 miles an hour x 6 hours = 33, 264,000 ; - ' = 1,663,200. 



2,376,000 



14. 



