A PERFECT LUBRICATING SYSTEM 81 



One has only to compare the older with the newer 

 models of motor cycles to see how makers have struggled 

 and are struggling to overcome the difficulties of lubrica- 

 tion. In the older models the driver was instructed to 

 give his machine a " pumpful " of oil from time to 

 time — every twenty minutes if he was making twenty 

 miles an hour ; more frequently in taking a steep hill, 

 less frequently when his machine was running easily. 

 The oil so injected found its way to the bottom of the 

 crank-case, where the whirling flywheel picked it up and 

 flung it into every corner of the engine — lubricating 

 piston, cylinder, and all the bearings of its machinery. 

 The system was laborious and wasteful ; with every 

 pumpful the engine passed from a surfeit to a dearth. 

 If the driver was forgetful or if a feed-pipe became 

 choked, the finest machine ran the risk of ruin. Then 

 came the " drip-feed " system, by which the joints were 

 given a steady supply of lubricant ; contrivances were 

 discovered by which the supply could be regulated accord- 

 ing to the need of the machine — greater when the engine 

 was running under stress, less when it was running easy. 

 But even then the system was far from perfect ; the 

 films of oil which coated the revolving shafts were not 

 uniform ; at the side of the joint where the greatest 

 pressure fell, the film was broken ; there the metal 

 surfaces were apt to touch and rub against each other. 

 Engineers have discovered only one way of overcoming 

 this difficulty, and that is by making the axle-boxes so 

 perfectly enclosed that oil can be forced into them by a 

 pump at such a pressure as will overcome that between 

 the shaft and its bearings, and thus interpose between 

 them a perfect coating or film of oil. No machine has 

 yet been fitted with a system which maintains a uniform 

 film of lubricant between the moving surfaces of its 

 joints except one, and that is the animal machine. We 

 can best study this perfect lubricating system in the 

 human body. 



We have already seen that hundreds of engines and 

 levers are used in the construction of the human machine. 



6 



