6 PRELIMINARY CONSIDERATIONS. 



One scientific division after another has been swept away 

 by the torrential stream of time. The theory of gravitation 

 furnished the first signal indication of the unity obtaining in 

 nature, and in recent days astro-physics and astro-chemistry 

 have further confirmed this. The doctrine of the conservation of 

 matter has been succeeded by the doctrine of the conservation 

 of energy. As a result of a series of discoveries ranging over 

 a century, we have recognised the feasibility of linking up most 

 of the main forces in nature heat, light, electricity, magnetism, 

 and, possibly, chemical affinity. Thus, again, it has been shown 

 that by lowering sufficiently its temperature, every gas can be 

 ultimately reduced to a liquid and probably to a solid, and that, 

 therefore, we have grounds for believing that the three states 

 of matter gaseous, liquid, and solid are due to definite calo- 

 rific differences. Once more, the boasted barriers between the 

 elements are gradually being removed. If carbon can exist in 

 four different states ; if oxygen can possess an allotropic form ; 

 if the arrangement of the elements in order of their atomic 

 weights evidences such striking relations between them that the 

 discovery of new elements having certain properties can be 

 predicted ; and if elements are actually produced by the trans- 

 mutation of other elements, it almost betokens intellectual ob- 

 stinacy to doubt that the day is approaching when the simple 

 chemical substances known to us will be proved to be com- 

 pounds of one element or compound perhaps of hydrogen, 

 perhaps of some lighter element yet unknown, who can tell? 

 Nor need we fear that the present-day telescope and microscope 

 have the last word to say in the exploration of the far-off 

 spaces and the more intimate structures of bodies. 



In biology the advance has not been less real, for the evo- 

 lution* of plant and animal life is now acknowledged universally, 

 and it is even exceptional to-day for any scholar to suggest 

 that man has not developed from a lower form. The old notion 

 of a vital chemistry has lost most of its scientific supporters, 

 and the struggle rages at the moment only round the mode of 

 the genesis of life itself. Who can doubt where the victory 

 will lie, if history and cumulative evidence are trustworthy 

 guides? The compartment theory unfortunately still holds the 



science suddenly dispelled, and the most barren and unpromising fields of 

 enquiry converted, as if by inspiration, into rich and inexhaustible springs 

 of knowledge and power on a simple change of our point of view, or by 

 merely bringing to bear on them some principle which it never occurred 

 before to try, will surely be the very last to acquiesce in any dispiriting 

 prospects of either the present or future destinies of mankind." (Sir John 

 Herschel, Discourse on the Study of Natural Philosophy, 1830, [5.].) 



