Page:Popular Science Monthly Volume 26.djvu/858

838 must be attributed to induced currents in the iron or steel, rather than to reversals of magnetism in molecular magnets. A later investigation upon the same subject tends to confirm the above result.

Among the instruments invented by Professor Trowbridge may be mentioned a new form of induction-coil, in which the primary coils are employed, and two induction-coils, the poles of the electro-magnets being connected by thin plates of iron. The spark produced from this combination by a mechanical break has great heating effect.

The active duties of a college professor leave little time for continued systematic investigation. A new era, however, is dawning in university education in America, and the college professor who shows ability for scientific investigation will undoubtedly be relieved of the yearly teaching of immature minds and be left free to devote himself to graduate students, to research, and to the general supervision of his department, rather than to the daily drill which should be left to trained assistants. Notwithstanding his full duties as a professor, Professor Trowbridge has published each year various investigations from the Physical Laboratory of Harvard University, which up to the present time has consisted of merely one room, inadequately fitted up for scientific work. In these investigations he has been often assisted by students. Among his researches are papers on the conveyance of heat by the electrical current in various metals, particularly in nickel; a paper written in association with Mr. C. B. Penrose, on the availability of a thermal junction for measuring very low temperatures; on the formation of vortex-rings in liquids, and an interpretation of the mathematical formulae relating to vortex rings in water; a paper by himself and Mr. Penrose, on the propagation of heat at right angles to, and in the direction of, the lines of magnetic force; a study of the effect of displacement of the compass in the Helmholtz's form of Gaugain galvanometer; a paper on the cause of the disturbances heard on telephone-lines, in which it was shown that a large part of their disturbances is due to the battery—earth. A survey of the country about Cambridge showed that the time-signals of the Harvard College Observatory were transmitted through the earth over a great extent of territory. This survey suggested to Professor Trowbridge the possibility of telegraphing across large bodies of water without a wire. Mr. Preece, of the London telegraphic system, acting upon the suggestion of Professor Trowbridge, succeeded in transmitting telegraphic signals from Southampton to the Isle of Wight, without a wire. Professor Trowbridge has also published various papers on thermo-electricity, a subject which has occupied his thoughts for many years.

The condition of the teaching of physics in the secondary schools having been brought to his attention by the want of preparation in this subject of students who present themselves for entrance to the university, Professor Trowbridge has prepared a treatise on