change of properties. Thus brandy and water, or gunpowder is a mixture. The properties of the brandy and of the water in the one case, and of the charcoal, nitre and sulphur in the other, are unchanged. A compound is the result of the union of two or more elements with change of properties; thus water is a compound of hydrogen and oxygen, and its properties are those of neither hydrogen nor oxygen. The fundamental distinction supposed to be at the basis of all chemical study, that between elements and compounds, is found to be inapplicable when we study such bodies as cyanogen, a compound of the two elements carbon and nitrogen, that behaves like an element. Ammonium, a compound of four atoms of hydrogen and one of nitrogen, also behaves like an element, taking the place of such metallic elements as potassium or sodium. In fact all the so-called "compound radicles" which enter so largely into our study of organic chemistry are groups of two or atoms of two or more elements that behave as simple bodies. The metals and the non-metals are connected by such forms as arsenic or selenium, placed by one chemist among the metals, by another among the non-metals. Hydrogen, usually classed with the non-metals, has the power of replacing metallic elements. It does this so persistently that, on theoretical grounds, chemists had long spoken of hydrogen as probably essentially a metal. When the French chemist Pictet succeeded in liquefying hydrogen, until then only known in the gas form, the liquid fell upon the floor of the laboratory with a metallic ring. And who is to say positively whether an alloy of copper and zinc is to be regarded as a mixture or as a compound of the two metals?

Still more important is the bridging over the supposed gulf between the inorganic and the organic chemical substances. A few years back this gulf was supposed to be great, fixed, impassable. The mineral or inorganic was makable by man. The organic was not, and never would be. The chemist might go on continually manufacturing hydrogen and oxygen, carbon dioxide, ammonia. But he was never to hope to make alcohol, sugar, urea, any of the multitudinous substances called organic. And now all this folly of forbidding is at an end. The organic bodies are manufactured by man. The inorganic and the organic are no more regarded as clearly distinguishable. Even the chemistry books by their very titles recognise and proclaim this fact. We have no longer works on organic chemistry. We have volumes on the chemistry of carbon compounds.

In geology the different kinds of rocks graduate into each other. Between the aqueous, or sedimentary, and the igneous, or those due to the action of fire, range the metamorphic, i.e., sedimentary rocks that have been afterwards subjected to heat. The various systems of sedimentary rocks are known now to be purely artificial if convenient divisions. From the Laurentian up to the recent rocks there has never been any real hiatus. Nowhere is there the slightest evidence of pause or of recommencement. Our groups are artificial. Nature is like Oallio and cares for none of these things.

Whilst rocks thus glide one into the other, the fossil remains that they contain do likewise. If the view of the special creationist were accurate we ought to find isolated forms of dead animals and plants, we ought to find sudden appearances in the rocks of forms not allied to these already encountered, we ought not necessarily to find a series of organic remains ascending in complexity of structure. If the view of the evolutionist is accurate, we ought to find no forms of dead animals or plants isolated; we ought never to find a form appearing without preliminary heralds of its coming in the shape of kindred forms; we ought to find a series of organic remains whose later members are in advance of the earlier. These latter expectations are realised.

In like manner the gap supposed to exist between the kingdoms of the non-living and living is closing up. As long as men had only studied the higher forms of living things