the electric furnace. "Before there can be applied science there must be science to apply," and it is in enabling the investigator to know Nature under a fresh aspect that electricity rises to its highest office. As a case in point, take the bolometer of Prof. S. P. Langley: its delicate wire, sensitive to one millionth of a degree centigrade, is moved by minute steps through the invisible areas of the solar spectrum; each indication of temperature, automatically photographed, comes out in a series of dark and bright lines. This process, repeated with each chemical element, promises that one day the physicist will have before him a full or tolerably complete map of every distinctive spectrum. He can then ask. Given such and such vibrations, how is the body constituted that sent them forth?—much as a musician might try to reason from the tone and timbre of a note to the structure of the instrument which uttered the note. In further uses of photography the physicist, by means of instantaneous contacts, is beginning to find out what goes on in the critical moments when chemical collisions in the voltaic cell are gliding into electric waves—an inquiry which bears on the prime question of electric art, namely, how the chemical energy contained in coal can be transformed into a current without the enormous levies imposed by the steam engine. Hertz, in the purely scientific excursion by which he generated electric waves intermediate in length between those of sound and light, came upon a discovery of profound interest—that, given its appropriate ray, every substance whatever offers it a free and open path. It remained for Prof. Röntgen to complete the proof that certain of these rays, while refusing obedience to the laws of light, can, nevertheless, exert photographic power. His apparatus combines in the happiest way the utmost resources of both the electrician and the photographer; at a vital point it employs the singular capacity for fluorescence whereby the compounds of barium and other substances can convert to visibility an otherwise invisible image. Apart from such a triumph as this, rich in possibilities for art and science, the common routine of ascertaining electrical constants has high value in research; to know the conductivity, polarizability, and other electrical properties of matter is to peer at its architecture through new windows; to detect many of the links which bind atom to atom, molecule to molecule. A new orchestration of inquiry is possible through the instruments created by the electrician, through the advances in method which these instruments suggest. Hence to-day a surround is in progress which may early in the twentieth century make atom and molecule as obedient to the chemist as brick and stone are to the builder now. But, however much new knowledge may do with electricity, some of its best work is already done. It is not likely in the fu-
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WHY PROGRESS IS BY LEAPS.