﻿400 Lecture-Room Demonstration of Atomic Models. 



by the average pole strength ±?n of each rod, which is 

 extremely uniform. A nucleus of positive charge ne may be 

 made up by taking 2n lengths of the same wire and inserting 

 them in a small glass or aluminium tube, as shown in fig. 5, 

 illustrating a nucleus of charge + 2e. In these circumstances, 

 each of the rods representing electrons is attracted to the 

 nucleus with a force varying nearly as the inverse square of 

 the distance and proportional to nm x m } the average pole 

 strength of each end of the rod being ztm. 



In order to realize this arrangement, the rods (about 

 7 cm. x 1 mm. diameter), representing negative electrons, 

 should be suspended from silk fibres about 1 metre or more 

 in length. By adjusting the position of the rods in the 

 space between the coils, a position of neutral equilibrium 

 may be found in which there is practically no tendency for 

 the rods to move either towards the centre or radially 

 outwards. Under the combined effect of gravity and of 

 the magnetic field they seem to float in any position. When 

 this adjustment has been made, the rods representing the 

 nucleus should be set in position along the axis of the coils. 

 The suspended rod representing the electron may then be 

 projected so as to describe a path about the fixed nucleus, 

 and a damped elliptic orbit will be observed, the nucleus 

 being at one focus. . 



If two lengths of wire are used to make up a nucleus -\-e 

 in the manner illustrated by fig. 5 (a), we obtain a model of 

 the hydrogen atom which is dynamically stable. 



If we make up positive nucleus of charge 2e, represented 

 by two pairs of iron rods, we obtain a model (fig. 5 (b)) 

 of the ionized helium atom which is dynamically stable. 

 If we introduce an additional iron rod representing an 

 electron (fig. 5), and therefore a complete helium atom, it 

 seems impossible to obtain a dynamically stable arrangement 

 by any circumstances of projection. For instance, any 

 attempt to reproduce the symmetrical oscillation suggested 

 by Langmuir meets with failure, owing to the dynamical 

 instability of this arrangement. 



It is obvious that further experiments along these lines, 

 leading possibly to results of great interest, might be carried 

 out by constructing large solenoidal coils to give a uniform 

 A.C. field, in which circumstances the inverse square law of 

 attraction and repulsion between electrons and nuclear 

 charges ne (n=l, 2, 3, etc.) would be faithfully reproduced. 



