12 The Realm of Nature CHAP. 



are apt to form the impression that Physics, Chemistry, 

 Astronomy, Geology, Geography, Meteorology, Biology are 

 definite sciences, distinct from each other, dealing with dif- 

 ferent orders of facts which are accounted for by independ- 

 ent theories. These sciences do not completely cover the 



FIG. i. Inter-relation of the Sciences. 



field of Nature as the coloured blocks of counties do the map 

 of England. They traverse the field rather like the railway 

 lines which radiate from London. The main line of each 

 science is distinct and easily followed, but the branches 

 interlace with one another in a very complex manner, and 

 though the network is very comprehensive, a mere fraction of 

 the vast surface is after all covered with the lines of definite 

 knowledge. The inter-relations of the sciences are shown in 



