4 Elementary Biology. 



fest impossibility. Consequently, when we define the next 

 three sciences of Physics, Chemistry, and Biology, as ' the 

 sciences of matter and energy,' we mean it to be understood 

 that they are limited to a consideration of the phenomena of 

 matter and energy as manifested, for the most part, on our 

 own earth. We say, * for the most part,' for within recent 

 years the method of spectrum analysis introduced by Bunsen 

 and Kirchhoff have enabled physicists and chemists to make 

 considerable progress towards the attainment of a knowledge 

 of the composition of the heavenly bodies ; whilst our belief 

 in the universal applicability of the laws of Physics has 

 become so firm that, although not submitted to the test of 

 actual experiment or even actual observation, we have no 

 hesitation in affirming that they hold sway in the farthest 

 removed of these bodies known to us. 



Physics may be defined as * the systematic exposition 

 of the phenomena and properties of matter and energy, in 

 so far as these phenomena and properties can be stated in 

 terms of definite measurement and explained by reference 

 to mechanical principles and laws ' (Daniell). Physics is 

 usually divided into two sections, the one dealing with the 

 phenomena and properties of masses of matter, the other 

 concerned with matter in its molecular aspect, and termed 

 molar and molecular physics respectively. The department 

 of molecular physics leads up to, and in some measure 

 overlaps, the science of Chemistry. 



Chemistry may be defined as the science which em- 

 bracss the study (1) of the properties of chemical ele- 

 ments, and of the compounds formed by the union of two 

 or more of them ; and (2) of the laws which regulate the 

 mutual action of elements and compounds on each other. 



We shall have occasion to discuss more fully in Chapters 

 I. and II. the general scope of Physics and Chemistry, more 

 especially with reference to the last of the three sciences of 

 matter and energy, namely, Biology. 



Biology, being 'the science which deals with the 



