ANIMAL MECHANICS. 



443 



Law I. Work proportional to weight. — The germ of this 

 Law is to be found in Borelli's great book, Yol. I., 

 Props, cxxi., cxxii., cxxiii. (pp. 209-211). 



I here give the statements of Borelli's Propositions. 



Proposition cxxi. 

 Si duo musculi ejusdem animalis fuerint ceque crassi, scilicet 

 compositi ex pari multitudine fibrarum, sed earum longitudines 

 incequales fuerint; suspendent quidem aiqualia ponder a : at po- 

 tential motives, et altitudines suspensionum eandem proportionem 

 habebunt, quam longitudines musculorum* 



Proposition cxxii. 

 Si vero, altitudines musculorum fuerint cequales, et crassities 

 eorum incequales : potential motivce, et ponder a suspensa, pro- 

 portionalia erunt crassitiebus musculorum ; atpondera ad cequales 

 altitudines ascendent. 



Proposition cxxiii. 



A t, si tarn altitudines, quam crassities musculorum incequales 

 fuerint, pondera suspensa erunt, ut crassities musculorum ; alti- 

 tudines elevationum eorum ut longitudines musculorum; at po- 

 tential compositam proportionem habebunt ex ratione crassitierum 

 et longitudinum. 



If in these Propositions we replace the phrase potentia 

 motiva by its modern equivalent, Work done, we obtain the 

 following statement : — 



The Work done by the contraction of a muscle is proportional 

 i to its length and area of cross section jointly. 



But it is evident, cceteris paribus, that the weight of a 

 muscle is proportional to the product of its length and cross 

 section ; so that Law I. may be fairly called Borelli's Law ; 

 although he failed to see the important consequences that 



