230 THE GOSPEL, AND THE SOCIAL CREED OF SCIENCE. 



juncture and constraint of the laws of heat, of motion, of 

 the expansive force of steam and its propelling power 

 upon a given movable mass ; all which laws, in addition 

 to others, are fulfilled in and by the machine, and are 

 made by it to work submissively and untiringly towards 

 one desired end. 



But to master and constrain Nature we must know 

 her, and we must obey her. We must have an accurate 

 knowledge of the law, a right estimate of the behaviour 

 of the forces that we use ; for the same force that will- 

 serve us submissively if we understand it, the same law 

 that will work our will if we go with it, will destroy us 

 without mercy in the opposite case. The first prelimi- 

 nary condition of Nature's service is knowledge that 

 we should study and know her, that we should learn the 

 sequences that Science has slowly gathered through the 

 centuries ; and where her laws admit of definite mathe- 

 matical measurement, that we should not mistake in the 

 application of our formulae or in the calculated strength 

 of materials, as otherwise our bridge will not bear the 

 strain upon it of possible forces, but breaks down ; our 

 vessel, with its centre of gravity placed too high, cap- 

 sizes in a sudden gale ; our lighthouse, with its foundation 

 sapped by the action of the waves, is blown down in a 

 storm. The condition next after knowledge that Nature 

 exacts is obedience. We must first know, we must next 

 obey; but these two conditions once fulfilled, there is 

 nothing that she may not grant us ; nothing that we 

 may not hope for, even marvels that cannot now be 

 dreamed of by us any more than the marvels of steam 

 and electricity by our ancestors a few generations back. 

 Already we have tamed and made all the great agencies 

 and forces of Nature our potent, though as yet only 

 partial, vassals. Heat, light, electricity, water, wind, and 



