74 



KNOWLEDGE & SCIENTIFIC NEWS. 



[April, 1905. 



"Ad Infinitunv.' 



The Structvire of the Atom. 



By Beresford Ingram, B.A. (Cantab.), F.C.S. 

 Prof. J. J. Thomson's lecture at the Royal Institution 

 on March 10 on " The Structure of an Atom " must 

 have been bewildering to an extreme to all those who 

 are not acquainted with the most recent developments 

 of science. 



To many of us an " atom " conveys but a very vagfue 

 idea. We think of it as something smaller than one of 

 those fine dust particles we see floating about in air 

 when a beam of sun-light enters a room. We are told 

 it has weight, but at the same time we are instructed 

 that we have no means of weighing it. A rea.sonable 

 conception of its size can be gained by imagining an 

 ordinary drop of water to be magnified to the size of 

 the earth, then the particles composing the drop would 

 be the size of cricket balls. 



Chemistry has taught us how these particles arrange 

 and behave themselves one to another, but physics 

 goes further than that, and proposes to show us of what 

 and how these particles are made up. 



Over ten j'cars ago Prof. Thomson proved that one 

 of these a/cms* of hydrogen is composed of one 

 thousand smaller particles. ' All these particles or 

 " corpuscles " have the same mass, and are similarly 

 charged with negative electricity. 



If this be so, then they must all repel one another. 

 This fact compelled the physicist to consider all these 

 particles being held together by a positive charge of 

 electricity, an assumption which, to some extent, was 

 warrantable by reason of the fact that positive elec- 

 tricity is always found associated with large masses of 

 mntter. 



Thus the simplest form of matter that can be 

 imagined is one of these negatively-charged corpuscles 

 being surrounded by a sphere of positive electrification. 



Before anything further can be known about the 

 atom we must find out how these corpuscles arrange 

 themselves when there is more than one in the atom. 



This is, to .some extent, experimentally demonstrated 

 by taking some short thin rods of steel and magnetis- 

 ing them. They are then stuck through corks, and so 

 arranged that when placed in water they will float 

 perpendicularly with their north poles uppermost out of 

 the water. In this way the magnets can move in one 

 plane only, i.e., that of the surface of the water; but it 

 must be borne in mind that the corpuscles composing 

 an atom are assumed to be free to move in any direc- 

 tion. 



When two such magnets are placed in water they, nf 

 course, assume some position apart from one another; 

 three form an equilateral triangle; four form a square, 

 five form a circle with the magnets at equal distances 

 from one another, six form a circle with one in the 

 middle. 



The following list shows how the magnets would 

 arrange themselves when thrown indescriminately into 

 the water, from which we conclude that such is their 

 position or arrangement of equilibrium. 

 No. of magnets 5, 7, 8, 9, 

 Outer ring . . 5, 6, 7. 8, 

 Innijlf^ing .. o, i, i, i, 



* An atom is defined as the smallest quantity of an element 

 which can enter into combination with any other element. 



The arrangement is found to be more stable, the 

 greater the number of magnets within the inner ring. 



Supposing an atom to contain twenty such particles, 

 then from the above table we could find out how they 

 arranged themselves. Look along the first line of 

 numbers and select the one nearest to twenty; it is 

 nineteen. This, as is observed, arranges itself twelve in 

 the outer ring and seven in the inner; there is still one 

 corpuscle over which would go within the inner ring 

 and increase the stability of the atom. Similarly, an 

 atom with 21 corpuscles would have twelve in the outer, 

 seven in the inner, and two in the inmost, and would 

 be even more stable than the atom with twenty 

 corpuscles. Twenty-two corpuscles would make a 

 more stable atom still. When, however, we get to 

 twenty-three corpuscles a new arrangement takes place 

 in which we get two rings only — thirteen in the outer 

 and ten in the inner. .As the number increases from 

 twenty-three to thirty, we get a whole series of bodies 

 with increasing stability (since the extra corpuscles arc 

 entering the area of the inner ring) until we come to 

 thirty, when we suddenly get another arrangement. 



But this is exactly what we get in the periodic classi- 

 fication of elements. .Starting with lithium, and taking 

 the elements in order, as their atomic weights increase, 

 we find we go from elements of marked electro-positive 

 nature to those of decided electro-negative, then 

 suddenly it reverts to an electro-positive element 

 and the gradation to the negative clement starts all 

 over again. 



Thus sodium, which marks the sudden reversion 

 from electro-negative to electro-positive elements, may 

 be considered as containing the arrangement necessary 

 to give lithium its electro-positive properties with 

 another ring (arrangement) or rings, that have no odd 

 corpuscles, added on to it. If, by any means, hereafter 

 to be discovered, the atom of sodium could be robbed 

 of its extra ring or rings, as a whole, we should expect 

 the transmutation of sodium to lithium to have been 

 effected. 



-So much, then, for the arrangement of the corpuscles 

 forming the atom; now let us turn our attention to the 

 behaviour of the atom itself. 



Even a superficial knowledge of chemistry would be 

 enough to force upon us the conviction that there 

 exists some constant law controlling the mo\cments of 

 the atoms composing an element. 



A study of the following experiment will show very 

 clearly that the atom does not obey any of the exi.sting 

 laws which are known to control matter. 

 Three electro - magnets are placed' as in figure, 

 / with their nortii 



poles pointing to- 

 wards a centre. 

 Between the an- 

 gles so formed 

 are placed three 

 vessels of water 

 which allow one 

 magnet to fioat 

 perpendicularly in 

 each, north pole 

 uppermost. The 

 magnets are so 

 arranged by guid- 

 ing wire that 

 they can only 

 move along a line which bisects the angles 

 between the magnets. Imagine, for the sake of illus- 

 tration, that the electro-magnets in the centre form a 



? 



