838 THE POPULAR SCIENCE MONTHLY. 



netism 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 con- 

 tinued 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 gi-aduate 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, par- 

 ticularly 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 formulse relating to vortex- 

 rings in water ; a paper by himself and Mr. Penrose, on the propa- 

 gation 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 com- 

 pass 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 bat- 

 tery — 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 sug- 

 gested to Professor Trowbridge the possibility of telegraphing across 

 large bodies of water without a wire. IMr. Preece, of the London 

 telegraphic system, acting upon the suggestion of Professor Trow- 

 bridge, succeeded in transmitting telegraphic signals from Southamp- 

 ton 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 experi- 



