: MECHANISM 



alive," but it is not a compliment to any human being to 

 describe him as " a mere machine." What the vital property 

 is, what we mean by the terms " life " and " living," no one 

 can exactly tell. About all we know of it is that some of the 

 commonest elements of matter (carbon, hydrogen, oxygen, 

 and nitrogen, with a little sulphur, phosphorus, and a few 

 other elements) frequently occur combined as living matter, 

 and that this living matter has marvelous powers of growth, 

 repair, and reproduction, besides a certain spontaneity, origi- 

 nality, and independence, which lifeless matter never displays. 

 " While there is life there is hope " for any plant or any ani- 

 mal, but this saying does not apply to any lifeless machine, 

 however complex or wonderful. 



2. The human body a living machine or mechanism. By 

 a machine we mean an apparatus, either simple or complex, 

 and usually composed of unlike parts, by means of which 

 power received in one form is given out or applied in some 

 other form. This power may be received, for example, in the 

 form of heat, or electricity, or muscular effort, or as the poten- 

 tial energy of fuel ; and it may be given out as heat, or elec- 

 tricity, or light, or sound, or as mechanical work, or in any 

 one of many other ways. One of the simplest of all machines 

 is a stove, an apparatus composed of a few simple parts by 

 means of which the potential energy or power of fuel 

 wood, coal, gas, or oil is liberated and applied as heat, for 

 warming or cooking. A lamp is a still simpler machine in 

 which the potential energy or power of gas or oil is liberated 

 and converted into useful light. A candle is a lamp so 

 simple that it almost ceases to be a machine, and yet the 

 wick is really an apparatus for securing proper combustion 

 of wax or tallow to provide good light. 



Machines of greater complexity are watches or clocks, 

 pieces of apparatus composed of many unlike parts which 

 receive power in comparatively large amounts for a short time 

 during the process of winding, store it as potential energy in 



