made up; hence Huygens concluded that Saturn could have but one satellite.
When chemistry emerged as a distinct branch of science from the superstitions and conceits which had so long overshadowed her, the line of demarkation between chemical and mechanical action was made clear and unmistakable. On this side were ranged all phenomena purely mechanical; on that, all phenomena purely chemical. Nature's laws must be simple. One great fact was predicated of each class of phenomena—the distinction was a simple distinction. But as Nature's facts were more thoroughly searched into, phenomena were remarked which tended to discredit the extreme simplicity of the division into chemical and mechanical actions; those phenomena were passed by as too trivial for serious notice. But the residual phenomena at last forced themselves upon the attention of chemists; and one great result of the examination of these phenomena has been the discovery that the simple classification into chemical phenomena on that side and mechanical on this was too simple—was, in fact, an artificial classification; that there is no sharp line of demarkation in Nature, but that a series of facts exists which bridges over the gulf formerly supposed to be fixed between the two sets of phenomena.
The earlier study of biological science tended to show a great simplicity in the vital processes occurring among all living things; but the more advanced study of the same science has altogether overthrown the simplicity of the earlier scheme. Certain animals, and classes of animals, seem deliberately to adopt strange expedients for reproducing their kind, as if to warn us against such hasty generalizations. How should we have imagined the possibility of fertilization for successive generations, of hermaphroditism, or of reproduction by fissure, etc., being found among the methods which Nature adopts for replenishing the earth, had we contented ourselves with an examination of the comparatively simple methods of ordinary sexual reproduction?
The importance of residual phenomena is undoubtedly great; the difficulties which attend the study of these phenomena are likewise great.
A phenomenon, supposed to be residual, may be found on closer examination to be fully explained by some known law, acting either under ordinary or under modified conditions. Before, therefore, attempting to find a new hypothesis which shall explain the residual phenomenon, it is necessary to determine the fact of the phenomenon being truly residual. Of course, if an explanation be found for the seemingly inexplicable phenomenon without the necessity of introducing a new hypothesis, a distinct step has been made in scientific advance. If, however, the phenomenon refuse to be explained by any known law, a new hypothesis must be found, or the old must be modified so as to admit of an explanation being given for the hitherto inexplicable fact.
Of the new hypotheses which present themselves to the mind, which
