290 THE HISTOEY AND SCOPE OF ZOOLOGY IX 



sciences includes Astronomy, Geology, Biology, and 

 Sociology. These sciences have for their aim to " ex- 

 plain" the concrete complex phenomena of (a) the 

 sidereal system, (h) the earth as a whole, (c) the living 

 matter on the earth's surface, (d) human society, by 

 reference to the jDroperties of matter set forth in 

 the generalisations or laws of the abstract -concrete 

 sciences, i.e. of mechanics, physics, and chemistry. 



The classification thus sketched exhibits, whatever 

 its practical demerits, the most important fact with 

 regard to Biology, namely, that it is the aim or busi- 

 ness of those occupied with that branch of science to 

 assign living things, in all their variety of form and 

 activity, to the one set of forces recognised by the 

 physicist and chemist. Just as the astronomer ac- 

 counts for the heavenly bodies and their movements 

 by the laws of motion and the property of attraction, 

 as the geologist explains the present state of the earth's 

 crust by the long-continued action of the same forces 

 which at this moment are studied and treated in the 

 form of "laws" by physicists and chemists, so the 

 biologist seeks to explain in all its details the long 

 process of the evolution of the innumerable forms of 

 life now existing, or which have existed in the past, 

 as a necessary outcome, an automatic product, of these 

 same forces. 



Science may be defined as the knowledge of causes ; 

 and, so long as Biology was not a conscious attempt 

 to ascertain the causes of living things, it could not 

 be rightly grouped with other branches of science. 

 For a very long period the two parallel divisions of 



