﻿Lecture-Room Demonstration of Atomic Models. 395 



The experiments are being- continued as time permits in 

 the hope of obtaining* some new information regarding these 

 free surfaces. Is is the intention to compare with thorium 

 the effects of one or two other tetravalent and trivalent 

 metals in the colloidal state. 



I wish to thank Professor J. C. McLennan for his kind 

 and encouraoino- interest in the work. 



XXXIX. Note on a Lecture-Room Demonstration of Atomic 

 Models. By Louis V. King, D.Sc, Macdonald Professor 

 of Physics, McGill University*. 



[Plate II.] 

 Section 1. 



SEVERAL mechanical models illustrating various types 

 of atomic structure have been proposed from time to 

 time. Among these we may mention Mayer's classical 

 experiments with floating and suspended magnets, illus- 

 trating the action of atomic forces t. 



Many modifications of these classical experiments have 

 been suggested. In particular, a paper by R. Ramsey de- 

 scribes interesting modifications of the original apparatus J. 



Actual apparatus illustrating the supposed structure of 

 atoms can now be obtained ready for use from scientific 

 instrument makers §. 



All these methods involve the repulsive forces between 

 steel elements (needles or spheres) in a permanent magnetic 

 field, together with the central attraction set up by a per- 

 manent magnet. An important point contributing to the 

 success of the experiment is that all the magnets, repre- 

 senting electrons, have as nearly as possible equal pole 

 strengths. Owing to magnetic reluctance and effects of 

 demagnetization, these conditions are difficult to realize in 

 practice without a considerable amount of care and ex- 

 penditure of time. 



* Communicated by the Author. 



t J. J. Thomson, ' Corpuscular Theory of Matter * (1907), Chapter 6, 

 pages 103 et seq. 



X It. R. Ramsey, "The Kinetic Theory of the Electron Atom." Pro- 

 ceedings of the Indian Academy of Sciences, 1918. Phil. Mag - , vol. xxxiii. 

 Feb. 1917, pp. 207-211. 



§ W. M. Welch, Scientific Company, Chicago. 



