1905.] 



on the Structure, of the Atom. 



51 



<^ 



years ago by an American physicist, Professor Mayer. The problem 

 of the structure of the atom is to find how a numl)er of bodies, which 

 repel each other with forces inversely proportional to the square of 

 the distance between them, will arrange themselves when under the 

 attraction of a force which tends to drag them to a fixed point. In 

 these experiments the corpuscles are replaced by magnetized needles 

 pushed through cork discs and floating on water. These needles 

 having their poles all pointing in the 

 same way repel each other like the 

 corpuscles ; the attractive force is 

 due to another magnet placed above 

 the surface of the water, the lower 

 pole of this magnet being of the op- 

 posite sign to the upper pole of the 

 floating magnets. This magnet at- 

 tracts the needles with a force directed 

 to the point on the water surface ver- 

 tically below the pole of the magnet. 

 The forces acting on the needles are 

 thus analogous to those acting on the 

 corpuscles in our model atom, with 

 the limitation that the needles are 

 constrained to move in one plane. 



As I throw needle after needle 

 into the water you see that they ar- 

 range themselves in definite patterns, 



3 magnets at the corners of a triangle, 



4 at the corners of a square, 5 at the 

 corners of a pentagon ; when, however, 

 I throw in the sixth needle this se- 

 quence is broken. The 6 needles do not arrange themselves at the 

 corners of a hexagon, but 5 go to the corners of a pentagon, and 1 goes 

 to the middle ; a ring of six with none in the inside is unstable. When, 

 however, I throw in a seventh, you see I get the ring of 6 with 1 in the 

 middle ; thus a ring of 6, though unstable when hollow, becomes stable 

 as soon as 1 is put in the inside. This is an illustration of the funda- 

 mental principle in the architecture of the atom : the structure must be 

 substantial. If you have a certain display of corpuscles on the outside, 

 you must have a corresponding supply in the interior ; these atonis 

 cannot have more than a certain proportion of their wares in their 

 windows. If you have a good foundation, however, you can get a 

 large number on the outside. Thus we saw that when the ring was 

 hollow, 5 was the largest number of needles that could be stable. I 

 place in the centre a large bunch of needles and you see that we get 

 an outer ring containing 22 needles in stable equilibrium. 



The proportion between the number which is in the outer ring 

 and the number inside required to make the equilibrium stable is 

 shown in the following table : 



Fig. 2. 



