396 



Dr. S. P. Thompson. A Physiological [-^-pr, 14, 



have done at first. We now stopped the water current for a time, in 

 the expectation of getting at the fundamental note of the animal by 

 eliminating the subordinate tones. It still responded, but very slightly, 

 to all the notes as before, but was unquestionably more sensitive about B flat 

 and A flat. 



I am, of course, aware that most of the preceding experiments may be 

 interpreted as either tactual or auditory reactions, and, if it is possible at all 

 to distinguish these two phenomena in the lower aquatic animals, the fact that 

 they are not necessarily auditory does not justify one in concluding, as some 

 recent observers have done, that they are therefore tactual. In the case, 

 however, of the experiments conducted on the physical table, it is, to my 

 mind, difficult to deny a true auditory sense to Gammarus. But this sense 

 (whatever its nature) seems to be extremely restricted, and only a few tones 

 appear to be appreciated. 



A Physiological Effect of an Alternating Magnetic Field. 

 By SiLVANUS P. Thompson, D.Sc, F.R.S. 



(Received April 4,— Read April 14, 1910.) 



Down to the present time it has been held by all physicists and by all 

 physiologists that magnetism produces no physiological effect either on the 

 human subject or on any living organism. Many persons have looked for 

 such effects. Lord Lindsay (now the Earl of Crawford), assisted by 

 Mr. Cromwell V. Varley, constructed many years ago an enormous electro- 

 magnet,* now in the Observatory at Edinburgh, so large that it would admit 

 between its poles the head of any person who wished to test whether a 

 strong magnetic field would have any sensible effect. Nothing whatever was 

 perceived as the result. 



I have, however, recently succeeded in demonstrating a real physiological 

 effect due to magnetism. Some six years ago, when experimenting with 

 an alternating electro-magnet which had. been constructed for showing 

 Prof. EHhu Tliomson's well-known exi)eriments on the repulsion of copper 

 rings, I observed a faint visual effect when my forehead was placed close to 

 the magnet. 



Recently, incited thereto by finding Lord Kelvin's mention of the negative 

 * See Lord Kelvin's ' Popular Lectures and Addresses,' vol. 1, p. 261, 



