PHYSICAL SCIENCE AND ITS CONNECTIONS. 3 



purpose of dividing the subject itself rather than for the 

 purpose of dividing it from other subjects. The properties 

 of matter and energy, of energy and ether, and of ether 

 and matter, are the subjects of investigation in physical 

 science. The matter and energy region is subdivided 

 into (1) pure dynamics of solids and fluids, that branch 

 where mathematics reigns supreme, whether we study the 

 motions of the planets, or of vortex rings, where we deal 

 with regular and reversible kinetic and potential energy ; 

 and (2) the study of irregular motions of heat and tur- 

 bulence, the kinetic theory of gases and the turbulent 

 motion of a liquid, the first and second laws of thermody- 

 namics, the laws of specific and latent heats, of temperature 

 and entropy, viscosity, and the limits of elasticity. This 

 subdivision into energy as regular and irregular is funda- 

 mental, and pervades the whole of science ; it bears on 

 cosmology when we study the action of tide production 

 and tidal retardation of rotation, the circulation of water 

 up the air and down the mountains and its erosions and 

 grindings ; it bears on chemistry when we study chemical 

 equilibrium and heat of chemical action ; it bears on bio- 

 logy when we study the regular production of mechanical 

 work, of electric currents, of nervous stimuli, and when 

 we study the production of heat, the viscous resistance to 

 Mow of fluids. The relations of ether and energy are com- 

 prised in the study of electro-magnetism and light. As 

 yet we know little about the relations of irregular energy 

 and ether, and still less how this bears on cosmology, che- 

 mistry and biology. The bearings of electro-magnetism 

 and light on the other branches of science are too many 

 to enumerate and too familiar to be worth enumerating. 

 We are yet only on the threshold of what is to be known. 

 The connections of matter and ether are even more ob- 

 scure. What is an electric current ? What is a magnet ? 

 Why are some things electro-positive and others electro- 

 negative ? Why do most vegetable substances turn the 

 plane of polarisation of light one way and animal sub- 

 stances the other way ? Why is terrestrial magnetism so 

 irregular, so variable ? On every side weak links require 



