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 color 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, cannot 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 of the size gives a spark ten times as strong as Franklin's; or the electrometers and galvanometers of Faraday with the mirror-galvanometers and electrometers of Sir William Thomson. Yet, at the same time, let such an observer think of the possibilities of the next fifty years, for the advance of science is not in a simple proportion to the time, and the next fifty years will probably see a far greater advance than the one hundred years since the date of Franklin's electrical work has seen. Is not the state of our imagination like that of the shepherd-boy who lies upon his back, looking up at the stars of heaven, and trying to imagine what is beyond the stars? The only conclusion is that there is something far more than we have ever beheld. Is it not the physicist of the future to have instruments delicate enough to measure the heat equivalent of the red and the yellow, the blue and the violet rays of energy?-instruments delicate enough to discover beats of light as we now discover those of sound an apparatus which will measure the difference of electrical potential produced by the breaking up of composite grouping of molecules? The photographer of to-day speaks, in common language, of handicapping molecules by mixing gums with his bromide of silver, in order that their rate of vibration may be effected by the long waves of energy. Shall we not have the means of obtaining the mechanical equivalent of such handicapped vibrations? Or, turning to practical science, let us reflect upon the modern transmitter and the telephone, and contrast these instruments with the rude, socalled lover's telephone, which consists of two disks connected by a string or wire. What an almost immeasurable advance we see here! Would it not have been as difficult for Franklin to conceive of the electrical transmission of speech as for the shepherd-boy to conceive of other stars as far beyond the visible stars as the visible stars are from the earth? Yes, we have advanced; but you will perceive that I have not answered the question, which filled the mind of Franklin, and which fills men's minds to-day, "What is electricity?" If I have succeeded in being suggestive, and in starting trains of thought in your minds which may enlighten us all upon this great question, I have indeed been fortunate. PAPERS READ. ON THE FRITTS SELENIUM CELLS AND BATTERIES. By C. E. In all previous cells, so far as I am aware, the two portions or parts of the selenium, at which the current enters and leaves it, have been in substantially the same electrical state or condition. Furthermore, the paths of the current and of the light have been transverse to each other, so that the two forces partially neutralize each other in their action upon the selenium. Lastly, the current flows through not only the surface layer which is acted upon by the light, but also through the portion which is underneath and not affected thereby, and which therefore detracts from the actual effect of the light upon the selenium at the surface. My form of cell is a radical departure from all previous methods of employing selenium, in all of these respects. In the first place, I form the selenium in very thin plates, and polarize them, so that the opposite faces have different electrical states or properties. This I do by melting it upon a plate of metal with which it will form a sort of chemical combination, sufficient, at least, to cause the selenium to adhere and make a good electrical connection with it. The other surface of the selenium is not so united or combined, but is left in a free state, and a conductor is subsequently applied over it by simple contact or pressure. During the process of melting and crystallizing, the selenium is compressed between the metal plate upon which it is melted and another plate of steel or other substance with which it will not combine. Thus by the simultaneous application and action of heat, pressure, chemical affinity and crystallization, it is formed into a sheet of granular selenium, uniformly polarized throughout, and having its two surfaces in opposite phases as regards its molecular arrangement. The non-adherent plate being removed after the cell has become cool, I then cover that surface with a transparent conductor of electricity, which may be a thin film of gold leaf. Platinum, silver, or other suitable material may also be employed. The whole surface of the selenium is therefore covered with a good (97) A. A. A. S., VOL. XXXIII. 7 electrical conductor, yet is practically bare to the light, which passes through the conductor to the selenium underneath. My standard size of cell has about two by two and a half inches of surface, with a thickness of Too to To inch of selenium. But the cells can, of course, be made of any size or form. A great advantage of this arrangement consists in the fact that it enables me to apply the current and the light to the selenium in the same plane or general direction, instead of transversely to each other as heretofore done, so that I can cause the two influences to either coincide in direction and action, or to act upon opposite faces of the selenium and oppose each other, according to the effect desired. By virtue of the process and arrangement described, my cells have a number of remarkable properties, among which are the following: 1. Their sensitiveness to light is much greater than ever before known. The most sensitive cell ever produced, previous to my investigations, was one made by Dr. Werner Siemens, which was 14.8 times as conductive in sunlight as in dark. In table A, I give results obtained from a number of my cells. It will be observed that I have produced one cell which was 1 Cells No. 23 and No. 129 are now in possession of Prof. W. Grylls Adams, of King's College, London; Dr. Werner Siemens has No. 25, and Prof. George F. Barker, of Philadelphia, has No. 26. 2 No. 24 was measured with a bridge multiplier of 6 to 1. |