man occupies an intermediate position in creation, with a microcosmos beneath, as far removed from the order of his perceptions as is the macrocosmos above him. To one who realizes what must be the complex dynamical relations as well as the order of magnitude of these molecular systems, the diagrams of molecular structure which may be seen in any work on organic chemistry can not but appear as crude and childish as the figures of constellations on a celestial globe; and when, as frequently happens, the student confounds the sign and the substance, one can hardly refrain from a little good-natured laugh at the spider-leg formulæ, as a noted German chemist is in the habit of calling them. Still, these are only the conventional forms of a good working theory, which is a noble product of human thought and an effective means of advancing knowledge.
For one who has followed the history of chemical thought from the first, it is easy to discover great imperfections in our present system. The assumption that, with more than seventy different kinds of atoms already known, uniting in such varied combinations to form molecules, only like molecules should ever aggregate to form material masses, is a solecism in the very postulates of the system; and the whole question of molecular combination is one which is still in abeyance. Analogy forbids us to believe that, down to a certain limit of dimensions that we call molecules, the constitution of matter is of a wholly different sort from that which appears on subdividing the molecules. It is an equally incredible assumption that all atoms of the same element are so many independent creations exactly alike in every respect. Then, as our knowledge increases, the distinctions between the chemical elements are becoming less marked and their relations to each other more intimate. They are beginning to appear, not as isolated units, but as links in a complex network, which presents an unbroken continuity throughout. The recent study of the rarer earths leaves us in doubt whether we have an indefinite number of elements, or only one under unnumbered manifestations; and the later results of spectrum analysis seem to indicate quite clearly that, at the high temperatures of the sun and of the fixed stars, many of our terrestrial elements are decomposed. From a mathematical analysis of the spectra, Grünwald maintains—and supports his conclusion by a great array of confirmatory measurements—that the remarkable solar spectrum line called helium, and the equally well-marked line of the sun's corona, come from two constituents of hydrogen gas, the first of which is somewhat heavier and the last far lighter than hydrogen gas; and this conclusion, if not finally accepted, is regarded as highly probable by men of such scientific sobriety as Liveing and Dewar, of Cambridge, in England—men who are acknowledged as among