THE PURPOSE OF DIVEHSITY 417 



elements, the wonderfully c'()ini)lr'x laws of tlioir combinations, 

 and the immense variety of their known eompounds, our ever- 

 increasing knowledge of the complexity of matter will he vory 

 much greater. 



During the early part of the nineteenth century, tlie old 

 idea of atoms as being indivisible, incompressible, and inde- 

 structible particles, almost universally prevailed. They were 

 usually supposed to be spherical in form, and 1<> 1m^ the scat 

 of both attractive and repulsive forces, leading to cohesion and 

 chemical combination. Those of the different elements were 

 supposed to differ slightly in size, and energy, which led to 

 their differences of weight and other properties. The whole 

 conception, though we now see it to be totally inadequate, was 

 comparatively simple, and with the help of the mysterious elec- 

 tric and magnetic forces seemed capable of explaining much. 



But, decade after decade, fresh discoveries were made ; chem- 

 ical theory became more and more complex; electricity, the 

 more it was known the less intelligible it became ; while a host 

 of new discoveries in the radiant forces of the ether seemed to 

 show that this mysterious substance was really the seat of all 

 the forces of the universe, and that the various basic forms of 

 matter which we term elements were nothing more than the 

 special manifestation of those forces. It thus became evident 

 that all our progress in physical science rendered the world of 

 matter far more wonderful, and at the same time less intel- 

 ligible than it had ever seemed to us before.^ 



1 The progress of modern chemistry well shows this increasing com- 

 plexity with increasing knowledge. The fact of carbon existing in three 

 distinct forms — charcoal, graphite, and diamond, each with its own special 

 physical and chemical characters — has already been referred to. Hut it 

 is found that many other elements have similar properties, especially sili- 

 con, phosphorus, arsenic, antimony, sulphur, oxygen, and several others. 

 This curious property is termed allotropy; and it seems somewhat analo- 

 gous to that property of many compound substances termed isomerism, of 

 which two striking examples were given at tlie beginning of the last 

 chapter. Another modern braneh of chemistry is the stuily of the relation 

 of crystallised substances to polarised light, which reveals nuiny new and 

 strange properties of identical compounds, and is termed iStcrcochcmistry. 



