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practice reaps by following in the path of theory. Railways and 

 all the ideas we associate with them existed a few years back but 

 in theory, and the whole aggregate achievements of the steam- 

 engine are but so much practice derived from the deductions of 

 theory. 



In conclusion, let me give you one or two examples of the 

 absurdities into which so-called practical men may be led from a 

 want of that theoretical knowledge which they affect so much to 

 despise. The action of the siphon has often been a source of 

 surprise to these so-called practical men. They have noticed that 

 before that instrument can be made to act, it is necessary that the 

 end from which the water is discharged should be at a lower level 

 than that at which it enters. From that they have concluded that 

 if the difference of level be sufficiently increased, water can be 

 made to run over any height whatever. Such an assertion I 

 have heard often by men of no mean so-called practical abilities. 

 Yet a very small amount of theoretical knowledge would speedily 

 convince them that increase the difference of level of the ends of 

 the pipe as we may, the water will only rise to a certain height. 

 After repeated, it may be expensive, failures they learn that truth. 

 Yet that is what is commonly called practice, but what I call 

 groping about in the dark. Again, it may be known'^to most of 

 you, that on some pit cages there is fixed a contrivance for the 

 purpose of preventing the fall of the cage should the rope break. 

 A common form of the apparatus is for two pairs of levers or 

 eccentrics to be fixed to the cage so as to be on opposite sides of 

 each guide. These levers or eccentrics are actuated by springs, 

 which are connected with the rope that is used to raise and lower 

 the cage. When the weight of the cage is on the rope, the action 

 of the springs is taken off the eccentrics or levers ; but immediately 

 the weight of the cage is taken off the rope, as for instance when 

 the rope breaks, then the springs act on the eccentrics or lever, 

 causing them to grip the guides, and thereby stop the cage from 

 falling. Now, I have seen a model of a cage and safety appartus 

 of this sort prepared by a man who was considered by some people 

 eminently practical, in which weights took the place of the springs 



