452 



TEACHINGS. 



MAN has unconsciously imitated Nature in the invention of 

 the Pulley, whereby the direction of force may be altered 

 almost at will. In this ease the cord takes the part of the 

 working tendon, and the Pulley of the fixed tendinous cross- 

 bar. There is much matter of interest in the tendons, but, 

 as our space is fast waning, I must resist the temptation of 

 describing them. 



IN all machinery one of the chief objects of the machinist 

 is to reduce friction as much as possible. He makes all the 

 joints as smooth as tools can polish, and always introduces oil 

 or some lubricating substance into the joints. Otherwise the 



TENDOXS OF HAND. 



engine rattles with a noise proportionate to its power, and 

 wastes its force on the friction. 



In my childish days a steam-engine of any kind used to 

 rattle so loudly that conversation was almost impossible. Now 

 they are made with such perfection, that the vast engines in use 

 at the pumping stations of the metropolitan drainage are almost 

 absolutely silent. 



There is the enormous hall, filled with gigantic beams and 

 rods, and cranks, and wheels. A single man turns a little 

 handle, and the whole machinery starts into life. Beams rock, 

 cranks and wheels revolve, rods slide up and down, and all in a 

 silence which is nearly appalling in its manifestation of 

 unassuming strength. Indeed, many a hand sewing machine 



