Page:Popular Science Monthly Volume 1.djvu/534

518 dynamical laws. By that common observation which precedes the more exact observations of science, we are taught that all the fragments, having risen to heights more or less various, will fall; that they will reach the ground at scattered places within a circumscribed area and at somewhat different times. Science enables us to say more than this. From those same principles whence are inferable the path of a planet or a projectile, it deduces the truth that each fragment will describe a curve; that all the curves, though individually different, will he specifically alike; that (ignoring deviations caused by atmospheric resistance) they will severally be portions of ellipses so eccentric as to be indistinguishable from parabolas—such parts of them, at least, as are described after the rush of gases ceases further to accelerate the fragments. But, while the principles of Mechanics help us to these certainties, we cannot learn from them any thing more definite respecting the courses that will be taken by particular fragments. Whether, of the mass overlying the powder to be exploded, the part on the left will be propelled upward in one fragment or several? whether this piece will be shot higher than that? whether any, and, if so, which of the projected masses will be stopped in their courses by adjacent objects they strike?—are questions it cannot answer. Not that there will be any want of conformity to law in these results, but that the data, on which predictions of them are to be based, cannot be obtained.

Observe, then, that, respecting a concrete phenomenon of some complexity, the most exact science enables us to make predictions that are mainly general, or only partially special. Seeing that this is so, even where the causes and effects are not greatly involved, and where the science of them is well developed, much more may we expect it to be so among the most involved causes and effects, the science of which is but rudimentary. This contrast, between the generalities that admit of prevision and the specialties that do not admit of prevision, will be still more clearly seen on passing from this preliminary illustration to an illustration in which the analogy is closer.

What can we say about the future of this newly-born child? Will it die of some disorder during infancy? Will it survive awhile, and be carried off by scarlet fever or whooping-cough? Will it have measles or small-pox, and succumb to one or the other? None of these questions can be answered. Will it some day fall down-stairs, or be run over, or set fire to its clothes; and be killed or maimed by one or other of these accidents? These questions also have no answers. None can tell whether in boyhood there may come epilepsy, or St. Vitus's dance, or other formidable affection. Looking at the child now in the nurse's arms, none can foresee with certainty that it will be stupid or intelligent, tractable or perverse. Equally beyond possibility of prediction are those events which, if it survives, will occur to it in maturity—partly caused by its own nature, and partly