98 THE REALITIES OF MODERN SCIENCE 



The question of how the electrons of an atom group 

 themselves under the action of their mutually repellent 

 forces and the attraction of the nucleus is a difficult 

 problem of mathematical physics. An interesting 

 study has been made, however, of the manner in which 

 a number of similar particles, which repel each other, 

 would group themselves in a plane, under the action 

 of a centrally located source of attraction. A number 

 of small magnetic needles were mounted vertically 

 through small corks and thus floated on the surface of 

 a vessel of water. Similar poles of the needles pro- 

 jected upward through the corks. A long magnet was 

 suspended vertically above the vessel so that a pole 

 of opposite character to those of the needles might act 

 as a center of attraction. It was found that the con- 

 figurations into which the floating poles grouped them- 

 selves depended upon their number. Thus three poles 

 placed themselves at the corners of an equilateral tri- 

 angle, the center of which was just below the attracting 

 magnet. Similarly four magnets group at the corners of 

 a square and five at the vertices of a regular pentagon. 



When six magnets enter into the configuration one 

 goes to the center, immediately below the pole of the 

 large magnet, the other five forming a pentagon. With 

 seven and eight similar figures are formed with one 

 magnet at the center. With nine there are two in the 

 center and seven in the outside ring. With ten or 

 eleven there is an inner triangle and an outer ring of 

 either seven or eight. The number in the center in- 

 creases until, when the total is fourteen, there is a pen- 

 tagon inside and a ring of nine outside. In other words, 

 as the number entering into the configuration is in- 



