electrical and magnetic effects. Such a person could then see the quick ebb and flow and interchanges of attractive forces as we now see the play of colors. Have you ever reflected that we may possibly have some day an electrical spectrum—perhaps I should call it an attracting-force spectrum—in which the electro-magnetic manifestations of energy shall be spread out and differentiated, just as that part of the energy which we receive from the sun and which we call light and heat is now dispersed in the visible solar spectrum? We regard to-day the manifestations of the different colors of bodies—the tints of the objects in the room—as the visible expression of the great law of conservation of energy. The energy which we have received from the sun is making interchanges and is modified by the different molecular structure of the different objects. Thus, a red body has absorbed, so to speak, certain wave-lengths of energy, and has transmitted or reflected back only the red or long waves of energy. The rest of the energy has been devoted to molecular work which does not appeal to us as light or even in certain cases as heat. If we suppose that radiant energy is electro-magnetic, can not we suppose that it is absorbed more readily by some substances than by others, that its energy is transformed so that with the proper sense we could perceive what might be called electrical color; or, in other words, have an evidence of other transformations of radiant energy other than that which appeals to us as light and color?
I have thus far conducted you over a field that, in comparison with what lies before us, seems indeed barren and churlish of results. Have we, then, nothing upon which we can congratulate ourselves? I can only reply by pointing to the rich practical results which you can see in the fine electrical exposition which we owe to the energy and liberality of the citizens of Philadelphia. Although we must glory in this exposition, it is the duty of the idealist to point out the way to greater progress and to greater intellectual grasp.
Perhaps we have arrived at that stage in our study of electricity where our instruments are too coarse to enable us to extend our investigations. Yet how delicate and efficient they are! Compare the instruments employed by Franklin, and even by Faraday, with those which are in constant use to-day in our physical laboratories. Franklin, by the utmost effort of his imagination, could not conceive, probably, of a mirror-galvanometer that can detect the electrical action of a drop of distilled water on two so-called chemically pure platinum plates, or of a machine that can develop from the feeble magnetism of the earth a current sufficiently strong to light the city of Philadelphia. Let him who wanders among the historical physical instruments of many of our college collections stand before the immense frictional electrical machine of Franklin's day, or gaze upon the rude electrometers and galvanometers of that time, and contrast Franklin's machine with the small Toepler-Holtz electrical machine which with a tenth
