i The Study of Nature 13 



Fig. i by representing each as a circle cutting all the others, 

 for on the outskirts of every science there are regions in 

 which another science shares the explanation of phenomena. 

 Chemistry, for example, is called in to aid astronomy in inter- 

 preting the spectra of the stars, to aid geology in explaining 

 the composition of rocks, to aid biology in determining the 

 changes of substance in living creatures. Physics or Natural 

 Philosophy in a sense includes every other branch of physical 

 science, although portions of Biology and Geography extend 

 beyond its limits. 



22. Physiography and the Special Sciences. By 

 division of labour the various parts of a watch are con- 

 structed by different workmen, and by the specialisation of 

 science the different realms of Nature are explored by 

 different investigators. In order to have a watch, however, 

 the results of divided labour must be combined, and in 

 order to have a just conception of the Universe the results 

 of specialised research must be fitted harmoniously together. 

 This is the function of Physiography, which has consequently 

 a unique value in mental training, being at once an in- 

 troduction to all the sciences and a summing up of their 

 results. It enables a beginner to obtain a quicker insight 

 into any of the special sciences and a fuller grasp of it, 

 while at the same time a student versed in any one special 

 science is enabled to appreciate far more fully than an 

 unversed one its relation to all others and to the system of 

 the Universe. 



23. Physiography and Nature. The natural Universe 

 may be compared to a gorgeous carpet of rich design. In 

 order to understand such a web we might follow out the 

 pattern thread by thread. Selecting first a red thread of 

 the weft, we notice how it passes above and below the 

 threads of the warp, across the fabric and back again, to 

 and fro until the end. Next a blue thread may be followed 

 in the same way, and so with all the separate colours. 

 The course of each thread has explained something, but the 

 results of all must be brought together to give a complete 

 explanation. In some such way each special science un- 

 ravels one of the threads of the Universe, but that thread is 



