CH. XLII. CONCLUDING REMARKS. 479 



group of insects ; and in this way discoveries of great value 

 have been made. 



On the other hand, great minds among us have taken up 

 the separate facts collected by specialists, and have woven 

 the whole of physical science into one grand scheme* Such 

 men as Faraday, Sir W. Grove, Stokes, Helmholt2, Sir W. 

 Thomson, and Clerk-Maxwell, together with many others, 

 have done their part in this work, so that now all the various 

 physical forces have been shown to be probably phases of 

 one great force appearing under many forms. For the future 

 no one physical force can be studied as if it existed by itself 

 alone, for each is shown to arise out of, and to pass into, 

 others. Heat, electricity, magnetism, chemical affinity, 

 motion all are related to each other, and we cannot call 

 any one of them the ruler over the rest. Like the colours on 

 the soap-bubble, they each take their turn in appearing and 

 disappearing, according to the conditions under which they 

 arise. Their relations are almost infinitely complex, and 

 we have still much to learn about them ; but the grand fact 

 that they pass the one into the other has been demonstrated 

 in our century ; and, under the names of ' the conserva 

 tion of energy,' and ' the correlation of the physical forces, 

 is one of the greatest results of modern science. 



The same tendency may be seen in the study of those 

 sciences which relate to life. Here, again, modern investiga- 

 tion links together the scattered observations of ages, and 

 unites them all in the theory of ' evolution,' or the gradual 

 unfolding of nature ; a theory which has been worked out 

 in all its details by Herbert Spencer, one of our greatest 

 living thinkers. In astronomy, indeed, we already catch 

 a glimpse of this law in the probable formation of the 

 heavenly bodies out of gaseous star-matter ; and in the or 

 game world we find it even more firmly held by scientific 



