that force, or energy, energy that can be measured, harnessed, made to do work, exists in matter, and that no satisfactory account of nature can be given which overlooks or neglects it. In these abstract theories we proceed from small beginnings and build up our theories upon conclusions which seem to be true. The great names connected with them are Newton, Lagrange, Fresnel and Helmholtz. In the concrete theories objects are found ready made. We take them as they are and seek to describe them, and give a reason for their distribution and for their existence. Hence the theory which occupies itself with forms, or the morphological theory. Nor is it less a matter of interest to know how these forms have originated, out of what materials and under what conditions. Hence the genetic theory, which is supported by an array of names the scientific world delights to honor. With the study of biology, or life, it is natural that there should be a vitalistic theory, and that in process of time the student should discover a border land between mind and matter subject in part to physical, in part to mental laws. So we have the psychophysical theory of the universe, and the deep and growing interest in the study of its problems. Yet however true each of these theories is, and there is truth in them all, it is certain that as science enlarges her borders, opens new fields of knowledge, these theories will be given up, or be modified to such an extent as to be virtually new, that the study of nature and her processes will continue to the end of time and that whatever advantages the man of science may have one thousand or ten thousand years hence, the problems then demanding solution will be neither less numerous nor less difficult than those which confront him to-day.
Yet these studies are of great value, not only for the practical benefit they bring to the world, but for the influence they have on those who pursue them. They teach men to be tolerant, for the fields to be traversed are so wide, the subjects considered are so varied and complex, and are cultivated with such diverse aims, that one can not be surprised at the different conclusions to which investigators, equally in earnest and equally competent, arrive. In a scientific mind dogmatism has no place. Love for old truth does not prevent hospitality toward that which seems to be new. Scientific studies are fitted by their very nature to produce enlargement of mind, clearness of vision and devotion to the search after truth. The man of science is not only far better prepared for his studies to-day by the mental attitude he is compelled to assume in beginning his special work than ever before; the equipment at his disposal is more complete and better adapted to his wants than his predecessors have enjoyed. Indeed, he is in this respect the heir of all the ages. It is his own fault if he is irreverent toward old truth, inhospitable toward that which is new, or lacking in devotion to search after that truth with which nature is full and is waiting to reveal.