448 THE APPLIED SCIENCES, 



seize their bearing, and to embody the idea which they suggested 

 in his machine. These improvements were, in fact, the results of 

 the most assiduous labour, aided by the most extensive knowledge. 

 The amount of the dilatation of water, in passing into the state of 

 vapour, the quantity of coal requisite to vaporise a given quantity 

 of the liquid, the amount of steam expended in each stroke of 

 an engine of known dimensions, and the elastic force of the 

 vapour itself at different temperatures, were all the subjects of 

 experimental research, and of rigorous calculation. It was thus 

 that he succeeded, step by step, in diminishing the quantity of 

 fuel necessary to produce a given effect. It was thus that he dis- 

 covered the means of alternately disengaging and absorbing the 

 steam, and of transmitting, with the smallest loss, the moving 

 power which he had thus developed. Finally, it was by the same 

 knowledge, and the same mechanical resources, that he succeeded 

 in applying the powerful instrument which he had contrived, and 

 modifying it for the accomplishment of the most opposite pro- 

 cesses. " Practical mechanics," says Sir John Herschel, " is, in 

 the most preeminent sense, a scientific art; and it may be truly 

 asserted, that almost all the great combinations of modern mecha- 

 nism, and many of its refinements and nicer improvements, are 

 creations of pure intellect, grounding its exertion upon a moderate 

 number of very elementary propositions in theoretical mechanics 

 and geometry." And the same may be said (though, of course, 

 in ever-varying degrees) of the relative position of the arts, in 

 general, and the physical sciences. The arts, in their highest 

 development, are but the applications of the powers of nature to 

 some practical object; and these powers must be known, the 

 uncontrollable laws of nature must be understood, before they 

 can be directed to the uses of life, and to the improvement of our 

 physical condition. 



But we have to deal with an objection of more weight. It 

 has been said, and it no doubt will be said, that skill in such opera- 

 tions as we have been speaking of is only to be acquired by practice ; 

 that the mechanical arts, and the arts of construction, are still arts, 

 a knowledge of whose processes must be learned by experience, and 

 by experience alone; and that it is only in the engine factory, or 

 in the field, that any solid information can be gained. 



Now, we freely grant that there is much that is true in this 

 statement, but, at the same time, we assert that it oversteps the 



