The progress of physics during 33 years (1875-1908) : four lectures delivered to the University of Calcutta during March 1908 / by Arthur Schuster.

  • Schuster, Arthur, Sir, 1851-1934.
Date:
1911
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Licence: In copyright

Credit: The progress of physics during 33 years (1875-1908) : four lectures delivered to the University of Calcutta during March 1908 / by Arthur Schuster. Source: Wellcome Collection.

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    mission of electro-magnetic effects with finite velocity. Everybody knows that the position of a delicately sus- pended magnetic needle is affected by a magnet which is placed in its neighbourhood, and if this magnet be shifted the needle will in general turn to one side. So far as our senses can judge, the action is instantaneous and the needle turns at the moment the magnet is displaced. But Maxwell says: No! not at the same moment but after a certain interval of time only, though this interval is too short to be apprehended by our senses. If the distance of the magnet be one metre the time of transmission of the effect would be the three hundred millionth part of a second. Can we obtain an experimental verification of this time of transmission ? Surprise may reasonably be expressed that while Maxwell was surrounded at the Cavendish Laboratory by a number of young physicists, who firmly believed in his electro-magnetic theory, no attempt was made by them to furnish an experimental proof of their master’s theoretical deductions. The explanation lies to a great extent in Maxwell’s habit of letting his students go their own way and find their own problems. Unless a student had asked him directly to suggest a problem, I doubt whether it would have occurred to him to give advice in the selection of a subject for investigation. Nevertheless,. and I speak from personal knowledge, the desirability of an experimental proof of Maxwell’s theory was realised by Cambridge men, and other British physicists, who were in contact with them, such as FitzGerald. But the experimental difficulties seemed formidable, notably as regards the emission of electro-