CONTRIBUTIONS FROM THE ROGERS LABORATORY 



OF PHYSICS, MASSACHUSETTS INSTITUTE 



OF TECHNOLOGY. 



LIL — A PHOTOGRAPHIC STUDY OF MAYER'S FLOATING 



MAGNETS. 



By Louis Derr. 



Presented February 10, 1909. Received January 13, 1909. 



Though Professor A. M. Mayer's beautiful experiment of floating 

 magnetized needles over a magnetic pole has been variously modified 

 in details, it has for many years been regarded chiefly as an interesting 

 study of a rather special set of forces ; but the recent investigations 

 into the structure and possible electrical nature of the atom have lent 

 a new interest to the equilibrium figures formed by the floating mag- 

 netic poles, and have suggested that they may illustrate the arrange- 

 ment of sub-atomic corpuscles, at least in the limited degree possible 

 in two dimensions. Mayer's original paper 1 gives drawings of 8 

 arrangements of 3 to 7 needles, and a later one 2 gives all the configur- 

 ations of 2 to 8 needles. A fuller discussion 3 gives a list of all the 

 configurations up to 51, with drawings up to 20 needles. Professor 

 R. W. Wood 4 showed that bicycle balls could be used, and gives 20 

 symmetrical figures. I have therefore thought it might be of interest 

 to assemble pictures of an entire series, in order to show the progression 

 from one form to another more clearly than can be done by tables ; and 

 the accompanying Plate is a reproduction from photographs of the 

 more stable forms assumed by the magnets when their number is varied 

 from 1 to 52. 



The magnets were clean quarter-inch steel balls, floated on freshly- 

 filtered mercury as described by Wood, but initially magnetized by 

 placing them one by one between the jaws of a powerful electromagnet. 

 Equilibrium figures may be obtained with unmagnetized balls, both 

 hard and soft ; but the magnetized balls are more easily managed, as 



1 American Journal of Science, 95, 276. 



2 Ibid., p. 477. 



3 Ibid., 96, 247. 



4 Phil. Mag., Ser. 5, 46, 162. 



