SCIENCE OF COMMON THINGS 33 



Muscular energy. Horse-power. Water-power. 



but none of these are capable of being used practically 

 for the production of motion. 



186 How is muscular energy exerted f 



Through the contraction of the fibres which constitute 

 animal muscles. The bones act as levers to facilitate 

 and direct the application of this force, the muscles 

 operating on them through the medium of tendons, or 

 otherwise. 



187 What animals possess the greatest amount of muscular power f 



Beasts of prey. Some very small creatures, how- 

 ever, possess muscular power in proportion to their 

 bulk, incomparably greater than that of the largest 

 and greatest of the brute creation. Kflea, considered 

 relatively to its size, is far stronger than an elephant or 

 a lion. 



188 In what method can a man exert the greatest active strength f 



In pulling upwards from his feet : because the 

 strong muscles of the back, as well as those of the up- 

 per and lower extremities, are then brought advan- 

 tageously into action. Hence the action of rowing is 

 one of the most advantageous modes of muscular action. 



189 What is'the estimate of the uniform strength of an ordinary man 

 for the performance of daily mechanical labor ? 



That he can raise a weight of 10 pounds to the height 

 of 10 feet once in a second, and continue to labor for 

 10 hours in the day. 



10O What is a " horse-power ?" We say a steam-engine is of a cer- 

 tain horse-power ; what is the meaning of the term ? 



The measure of a" horse's power" adopted as a 

 standard for estimating the power of steam-engines, is 

 that he can raise a weight of 33,000 pounds to the 

 height of one foot in a minute. 



191 What is the strength of a horse compared with that of man f 



The force of one horse is considered to be equal to 

 that of five men. 



193 What do we mean by " water-power f" 



The power obtained by the action of water, applied 

 generally to the circumference of wheels, which it 



