514 PHYSIOLOGY AT THE FAEM. 



of the horse, 20 + 28 + 8 = 56 the number of ounces which 

 Dr Playfair gives, the fractions omitted. In his comparison 

 between the food and labour of the ox and horse, the flesh- 

 formers of the food of the ox namely, mangold-wurzel, 

 beans, and wheaten straw are found thus, though the total 

 of flesh-formers is larger in our calculation, owing to some 

 slight difference in the estimate given of these in the tables 

 made use of in this work. The proportion of flesh-formers in 

 mangold-wurzel is, according to Cameron, 3 per cent ; hence 

 100 : 3 :: (50 Ib.) 800 oz. : 24 oz. The proportion of flesh- 

 formers in beans, according to Playfair, is, as above, 27 per 

 cent; hence 100 : 27 : : (3 Ib.) 48 oz. : 12.96 oz. The pro- 

 portion of flesh-formers in wheat-straw is, according to John- 

 ston, 1.6 per cent; hence 100 : 1.6 : : (17 Ib.) 272 oz : 4 ; 

 whence the sum of these three results is 24 + 12 + 4 = 40 oz. 

 With respect to the estimate made of the work of the horse 

 in foot-pounds, and the like estimate of the food of the ox, a 

 few words are required. A foot-pound is by no means a happy 

 expression. It belongs altogether to the new doctrine of the 

 " conservation of energy/' A foot-pound is the energy required 

 to raise a pound weight one foot. The fall of a pound weight 

 through the space of one foot, friction apart, is sufficient to 

 raise the same weight one foot. This fact is exemplified in 

 the pendulum, in which a ball of a pound weight, by the im- 

 pulse it receives in descending, is thrown upwards on the op- 

 posite side of the line of gravitation. As mentioned before (p. 

 496), a pound weight of water, in falling through 772 feet, ac- 

 quires an additional temperature of one degree Fahrenheit. 

 This number, then, 772, is accounted the mechanical equivalent 

 of heat that is, the heat required to raise a pound of water one 

 degree Fahrenheit is sufficient to raise a pound weight of mat- 

 ter 772 feet, or, what is the same thing, 772 pounds of matter 

 through one foot ; and this last fact is expressed by saying 



