Page:Popular Science Monthly Volume 45.djvu/588

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supplies in the winter quarters. The northward movement of all the others must be through some impulse not yet ascertained. In many other instances it is not dependent on the weather at the moment. This is especially the case with sea birds. Prof. Newton observes they can be trusted as the almanac itself. Foul weather or fair, heat or cold, the puffins—Fratercula arctica— repair to some of their stations punctually on a given day, as if their movements were regulated by clockwork. In like manner, whether the summer be cold or hot, the swifts leave their summer home in England about the first week in August July occasional stragglers ever being seen after that date. To say that migration is performed by instinct is no explanation of the marvelelous faculty; it is an evasion of the difficulty. The sense of sight can not guide birds which travel by night, or span oceans or continents in a single flight. In noticing all the phenomena of migration there yet remains a vast untilled region for the field naturalist. What Prof. Newton terms the sense of direction, unconsciously exercised, is the nearest approach yet made to a solution of the problem. He remarks how vastly the sense of direction varies in human beings, contrasting its absence in the dwellers in towns compared with the power of the shepherd and the countryman, and, infinitely more, with the power of the savage or the Arab.

Chemical Constitution and Color.—A curious side light, says Prof. James Emerson Reynolds, seems to be thrown on the nature of the elements by the chemico-physical discussion of the connection existing between the constitution of certain organic compounds and the colors they exhibit. We may take it as an established fact that a relation exists between the power which a dissolved chemical compound possesses of producing the color impression within our comparatively small visual range, and the particular mode of grouping of its constituent radicals in its molecule. Further, the reality of this connection will be most freely admitted in the class of aromatic compounds—that is, in derivatives of benzene, whose constituents are so closely linked together as to exhibit quasi-elemental persistence. If, then, the possession of what we call color by a compound be connected with its constitution, may we not infer that "elements" which exhibit distinct color, such as gold and copper, in thin layers and in their soluble compounds, are at least complexes analogous to definitely decomposable substances? This inference, while legitimate as it stands, would obviously acquire strength if we could show that anything like isomerism exists among the elements; for identity of atomic weight of any two chemically distinct elements must, by all analogy with compounds, imply dissimilarity in constitution, and therefore definite structure, independently of any argument derived from color. Now, nickel and cobalt are perfectly distinct elements, as we all know, but, so far as existing evidence goes, the observed differences in their atomic weights (nickel, 58·6; cobalt, 58·7) are so small as to be within the range of the experimental errors to which the determinations were liable. Here, then, we seem to have the required example of something like isomerism among elements, and consequently some evidence that these substances are complexes of different orders; but in the cases of cobalt and nickel we also know that in transparent solutions of their salts, if not in thin layers of the metals themselves, they exhibit strong and distinct colors—compare the beautiful rosy tint of cobalt sulphate with the brilliant green of the corresponding salt of nickel. Therefore, in exhibiting characteristically different colors, these substances afford us some further evidence of structural differences between the matter of which they consist, and support the conclusion to which their apparent identity in atomic weight would lead us. By means of such side lights we may gradually acquire some idea of the nature of the elements, even if we are unable to get any clew to their origin other than such as may be found in Crookes's interesting speculations.

The Camphor Tree.—While camphor was formerly produced in Sumatra, Borneo, and other parts of the East Indies, all now known to the trade comes from Japan and Formosa. The camphor tree is a large evergreen of symmetrical proportions, somewhat resembling a linden. It bears a white flower which ripens into a red berry. Some of the