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 - E, communication, distribution, shock, ignition, analysis, charging, isolation, discharging, electric current, &c. &c., to this schema we are able to reduce and even to direct the effect; but of the process itself we know nothing: that remains an _x_. Here therefore cause and effect are completely heterogeneous, their connection is unintelligible, and we see bodies show great susceptibility to causal influences, the nature of which remains a secret for us. Moreover in proportion as we mount higher in the scale, the effect seems to contain more, the cause less. When we reach organic Nature therefore, in which the phenomenon of life presents itself, this is the case in a far higher degree still. If, as is done in China, we fill a pit with decaying wood, cover it with leaves from the same tree as the wood, and pour a solution of sulphur repeatedly over it, an abundant crop of edible mushrooms will spring up. A world of rapidly moving _infusoria_ will arise from a little hay well watered. What a difference lies here between effect and cause! How much more does the former seem to contain than the latter! When we compare the seed, sometimes centuries, nay even thousands of years old, with the tree, or the soil with the specifically and strikingly different juices of innumerable plants--some healthy, some poisonous, some again