1901.] 



and Melting Points to Atomic Mass. 



23 



of lines belonging to elements of low atomic mass, such as hydrogen, 

 helium, and lithium, than for the others. The differences between the 

 observed and calculated numbers increase in magnitude with the 

 atomic mass. 



The suggestion to take the highest value of fi, that derived from the 

 more refrangible lines, as the starting point, appears to be perfectly 

 fair. When this is done, we observe that the differences between the 

 numbers calculated with this /x as a constant for the series and the 

 observed numbers increase with the intensity of the lines. There is, 

 it appears, some disturbing influence introduced along with the causes 

 which increase the intensity of the lines. This disturbing influence 

 retards the rate of vibration, and its effect becomes more marked as 

 the atomic mass increases. It is now possible to determine the amount 

 of the disturbance produced in this way, and to compare it with the 

 disturbance produced by increases in the atomic mass. 



The metals of the alkalies have closely allied chemical and physical 

 properties ; but the three metals, potassium, rubidium, and caesium, 

 are more closely related to one another than to lithium and sodium. 

 The spectra of these three metals may be said to agree almost line for 

 line, but the spectra of lithium and sodium are moved considerably 

 towards the more refrangible end of the spectrum : the corresponding 

 vibrations are much faster in lithium and sodium. The effect of 

 increase of atomic mass in these groups is to diminish the oscillation 

 frequency of the lines, and the rate of change is much greater in 

 passing from lithium to sodium and potassium than from potassium to 

 rubidium and caesium. 



These facts appear to indicate that there is something besides the 

 molecule of the element involved in the production of the lines under 

 consideration. The late Professor Rowland, remarked, in an address 

 on "The Highest Aim of the Physicist "* : — " We know of little or no 

 etherial disturbance which can be set up by the motion of matter 

 alone : the matter must be electrified, in order to have sufficient hold 

 on the ether to communicate its motion to the ether." This fact 

 suggests the view that the influence outside the molecule is the 

 portion of the aether affected by the motion of the electrified molecule : 

 that this portion of aether acts as a load on the molecule (or it may 

 be that the molecule acts as a load on the aether), the effect in the 

 end being that the spectral lines in the series we have been considering 

 are produced by the mutual action of the matter and the aether. 



This suggestion seems to offer an explanation for the retardation 

 which increases with the intensity of the members of the series. It 

 would appear that the intensity of the line is proportional to the 

 amount of the aether affected, and as the load is greater so is the 

 retardation of the vibrations greater. 



* 1 Amer. Jour. Sci.,' December, 1899, p. 406. 



