14 THE ROYAL SOCIETY OF CANADA 



This is of course Planck's assumption, and it is certainly unexplained 

 and probably not in accord with Hamilton's equations as deduced 

 from Newton's Laws. Nevertheless any day we may learn why 

 energy is emitted per saltum, and this mystery will vanish. 



Now if you permit these somewhat arbitrary assumptions to 

 Bohr, he can and does deduce, at least for the lighter atoms such as 

 hydrogen and helium, the Rydberg formula for the spectral series. 

 He finds — 



2^-2 me* / 1 1 \ 



where n is the frequency; m,e mass and charge of an electron, h is 

 Planck's constant: a,b, are integers. The quantity before the bracket 

 should equal the Rydberg number N of observed value 3-29X10 15 . 

 Bohr's calculated value is 3-26X10 15 , showing a most satisfactory 

 agreement. 



Bohr endeavours to account for the manner in which two hydrogen 

 atoms form a molecule. Each atom has a nucleus of positive charge 

 and a simple electron revolving around it. Their charges are equal 

 and opposite. The nuclei of two such atoms repel each other. The 

 revolving electrons of two atoms close together, if rotating in the 

 same direction, constitutes two parallel currents of electricity, and these 

 attract one another and arrive in the same plane. It is easy to make 

 a model on a whirling table with the nuclei on an upright rod, the 

 electrons revolving like the governor balls of an engine. Bohr 

 has gone further, and conceived a similar model of a water molecule 

 with the two nuclei of hydrogen and one nucleus of oxygen in a straight 

 line, with 10 electrons revolving in their zones around them. No 

 doubt these suggestive schemes are somewhat speculative, but it 

 is refreshing to find a first approximation to a dynamical scheme 

 replacing the old unsatisfactory electrostatic atoms, which probably 

 did not approximate to the truth. Some of the formidable organic 

 molecules must have a complexity which it may take generations of 

 physicists to unravel. 



(11). One of the triumphs of mathematical physics was the 

 forecast of Laue that crystal bodies have their atoms so distributed 

 that Rôntgen rays must- be diffracted by these atoms in the same 

 manner that closely ruled crossed lines on a glass plate diffract visible 

 light. This forecast and its rapid verification, enabled the two 

 Braggs, father and son, to measure with accuracy the wave lengths 

 of Rôntgen rays. While the waves of invisible light are of the order 

 10" cm., those of Rôntgen rays are of the order 10 -8 cm. or about 

 one thousandth of the former. The electromagnetic theory recognizes 



