NATURAL SCIENCE TO GENERAL SCIENCE. 23 



perimental sciences have one great advantage over the 

 natural sciences in the investigation of general laws of 

 nature : they can change at pleasure the conditions under 

 which a given result takes place, and can thus confine 

 themselves to a small number of characteristic instances, 

 in order to discover the law,. Of course its validity must 

 then stand the test of application to more complex cases. 

 Accordingly the physical sciences, when once the right 

 methods have been discovered, have made proportionately 

 rapid progress. Not only have they allowed us to look 

 back into primaeval chaos, where nebulous masses were 

 forming themselves into suns and planets, and becom- 

 ing heated by the energy of their contraction ; not only 

 have they permitted us to investigate the chemical con- 

 stituents of the solar atmosphere and of the remotest 

 fixed stars, but they have enabled us to turn the forces of 

 surrounding nature to our own uses and to make them the 

 ministers of our will. 



Enough has been said to show how widely the intel- 

 lectual processes involved in this group of sciences differ, 

 for the most part, from those required by the moral 

 sciences. The mathematician need have no memory 

 whatever for detached facts, the physicist hardly any. 

 Hypotheses based on the recollection of similar cases may, 

 indeed, be useful to guide one into the right track, but 

 they have no real value till they have led to a precise and 

 strictly defined law. Nature does not allow us for a moment 

 to doubt that we have to do with a rigid chain of cause 

 and effect, admitting of no exceptions. Therefore to us, 

 as her students, goes forth the mandate to labour on till we 

 have discovered unvarying laws ; till then we dare not rest 

 satisfied, for then only can our knowledge grapple victo- 

 riously with time and space and the forces of the universe. 



The iron labour of conscious logical reasoning demands 

 great perseverance and great caution; it moves on but 



