THE WILL IN NATURE.
they differ as to quantity, as in the lever, mere Space and Time relations suffice to make the thing clear. But as soon as weights come also into play, a second mysterious element supervenes, gravity: and, where elastic bodies are concerned, elasticity also. Things change as soon as we begin to ascend in the scale of phenomena. Heat, considered as cause, and expansion, liquefaction, volatilization or crystallization, as effects, are not homogeneous; therefore their causal connection is not intelligible. The comprehensibility of causality has diminished: what a lower degree of heat caused to liquefy, a higher degree makes evaporate: that which crystallizes with less heat, melts when the heat is augmented. Warmth softens wax and hardens clay; light whitens wax and blackens chloride of silver. And, to go still further, when two salts are seen to decompose each other mutually and to form two new ones, elective affinity presents itself to us as an impenetrable mystery, and the properties of the two new bodies are not a combination of the properties of their separate elements. Nevertheless we are still able to follow the process and to indicate the elements out of which the new bodies are formed; we can even separate what has been united and restore the original quantities. Thus noticeable heterogeneousness and incommensurability between cause and effect have here made their appearance: causality has become more mysterious. And this becomes still more apparent when we compare the effects of electricity or of the Voltaic pile with their causes, i.e. with the friction of glass, or the piling and oxidation of the plates. Here all similarity between cause and effect at once vanishes; causality becomes shrouded in a thick veil, which men like Davy, Faraday and Ampère have strenuously endeavoured to lift. The only thing now discernible through that veil, are the laws ruling its mode of action, which may be brought into a schema such as +E and —E, communication
PHYSICAL
