a healthy distrust of our theories, and an abiding faith in that pillar of cloud by day and the pillar of fire by night—the doctrine of the conservation of energy.
Having thus outlined the present condition of our knowledge, and of our comprehension of the bearing and tendencies of physical science, let us strive, with the most powerful instruments we have, to survey the promised land which is undoubtedly to be the possession of those who come after us. It is one thing to become familiar with all the applications of the mechanical theory of electricity, and another to make an advance in the subject so that we can see the relations of electrical and magnetic attraction to the attraction of gravitation and to what we call chemical attraction. To this possible relationship I wish to call your attention to-day.
I am forced to believe that the new advances in our knowledge of electrical manifestations are to come from a true conception of the universality of electrical manifestations, and from the advance in the study of molecular physics. Picture to yourselves the position of an investigator in this world. A person on the moon could only conceive of this audience as a molecule made up of many atoms. He could not measure the energy you manifest by moving about—the heat energy—the electrical energy due to the friction of your envelopes. Indeed, he could only suppose your existence, just as we imagine the existence of a molecule of a crystal. Now, the distances we force molecules apart by many of our chemical processes seem extremely small to us; but how immense they really are compared with the distances apart of the atoms! Is it not as if we should take a stone from the moon or from Venus and place it upon the earth in the time of one second? You can imagine, from the familiar spectacle of a meteor, the heat and the electricity that would result. Yet, in respect to relative distances, do we not do something similar when we break a crystal or pour acid upon a metal, or strike a dynamite-cartridge? We are infinitely small ourselves compared with the great universe about us; yet our task is to comprehend the motions of aggregations of atoms infinitely smaller than that aggregation which we call man.
When we break a crystal mechanically, we have a development of electricity. When we heat certain crystals—tourmaline, for example—besides the strain among the molecules of the crystal which is produced by the increased rates of vibration, we have a difference of electrical potential. When we let an acid fall from the surface of a metal, the metal takes one state of electrification and the drop of acid the other—in other words, we produce a difference of electrical potential. On the other hand, a difference of electrical potential modifies the aggregation of molecules. The experiments of Lippman are well known to you. He has constructed an electrometer, and even an electrical machine, which depend upon the principle that the superficial energy of a surface of mercury covered with acidulated water is modified
