82 SCIENCE REMAKING THE WORLD 



In the helium atom we have the characteristic struc- 

 ture of all atomic systems. At the centre there is a 

 nuclear particle composed of a close arrangement of 

 protons and electrons but including more protons than 

 electrons. In the region beyond there are electrons. 

 The whole constitutes a miniature celestial system in 

 which the nucleus is the central mass and the remaining 

 electrons planetary satellites. 



Atomic structure is more completely illustrated by 

 the familar nitrogen of which we daily breathe about 

 four times as much as we do of oxygen. Its nucleus 

 contains seven more protons than electrons; in fact 

 fourteen protons and seven electrons. About this 

 nucleus are seven planetary electrons. Two of these 

 apparently occupy positions on opposite sides like the 

 satellites in the helium atom; and the remaining five, 

 at a greater distance from the nucleus, are disposed as 

 if on an imaginary sphere about the nuclear centre. 



How much of this well-ordered picture is speculation? 

 Relatively little. Admitting that the evidence is not 

 direct but circumstantial and that the positions of the 

 planetary electrons are not exactly known, the state- 

 ment stands as made. The evidence, however, may 

 well wait the presentation of further facts and some 

 ideas as to the magnitudes involved. 



Imagine this atom of nitrogen which consists of seven 

 specks in space enclosing imperfectly a central speck, 

 for the atom is mostly hole imagine it magnified about 

 one hundred thousand times. The specks would then 

 be about as large as the unmagnified atom. Two such 

 atoms of nitrogen, associated much like partners in 



