54 THE ROYAL SOCIETY OF CANADA 



prevents the magnetic forces arising from the motions of the electrons, 

 from forming a system of closed lines of force within the atom itself." 

 Bohr believes that the development of our ideas of atomic structure 

 as we pass from one element to another will be greatly advanced by a 

 careful analysis of the magnetic properties of the atoms and ions. 



If, however, a curve is plotted between the magnetic suscepti- 

 bilities and the atomic numbers of the elements, it will be found that, 

 aside from the fact of their periodicity, the two curves have little in 

 common, for the maxima of the susceptibility curve will be at those 

 atomic numbers which are almost at the very minima of the atomic 

 volume curve. There is practically no similarity in shape of the two 

 curves and for that reason it has been omitted from the paper. 



From the standpoint of Langevin's Theory of Magnetism it 

 might be expected that diamagnetism, being a fundamental property 

 of the atom, should exhibit some close relation with atomic number. 

 With many of the elements, as such, the inherent basic diamagnetism 

 is masked by the much larger effect of paramagnetism and this fact 

 complicates a study of this property. Realizing this, St. Meyer, 

 Pascal and others attempted to determine the diamagnetic sus- 

 ceptibilities of the atoms themselves from an examination of their 

 compounds. It was found that an element in the pure state might 

 be quite paramagnetic and yet in all its compounds it might have a 

 certain amount of diamagnetism. It must be remembered, too, that 

 in compounds we are dealing with two or more nuclei, sharing some 

 of their electrons in common electronic orbits, which is quite a different 

 arrangement from what is the case in the elements themselves which 

 are believed to be mostly monatomic. There is no doubt that, though 

 in the case of compounds it is more correctly a question of the magnetic 

 properties of the ion rather than of the atom, in some cases, about 

 18 in all, there is good agreement of the values of the atomic magnetic 

 susceptibility obtained in both ways but these are scattered through 

 the periodic system in no definite way. 



Part II — The Atomic Diameters of the Elements. 



In the development of the theory of magnetism there have been 

 repeated attempts to explain the magnetic phenomena by the physical 

 interpretation of what are called molecular magnets. First Ampere 

 and then Weber, at a time when little or nothing was known of the 

 constitution of the atom, tried to solve the problem by the assumption 

 of the existence of currents flowing within the atoms or molecules. 

 Recent developments of the theory of electrons by J. J. Thomson, 



