1901.] 



and Melting Points to Atomic Mass. 



17 



ordinates representing the elements with the lowest atomic masses are 

 very close to the ordinate representing zero atomic mass. 



It may be remarked that, even if it could be shown positively that 

 the lines do not intersect on the line of zero atomic mass, they must 

 intersect in points very near to it. Any disturbing influence must be 

 so small that the statement may be accepted as a broad fundamental 

 fact, as far as the elements under consideration are concerned. 



(5.) The form of some of the connecting lines indicates that no 

 element will be found of greater atomic mass than the greatest 

 represented. This is seen most strikingly in the connecting 

 lines of copper, silver, and gold. 



The Homologous Series of Spectral Lines. 



Eydberg has classed together as " Lines of Type I," the series found 

 in the spectra of hydrogen, helium, lithium, oxygen, sodium, magne- 

 sium, aluminium, sulphur, potassium, calcium, copper, zinc, selenium, 

 rubidium, strontium, silver, cadmium, indium, caesium, mercury, and 

 thallium. To these may be added gallium. 



The series have been further divided into three kinds : the principal 

 series and two subordinate series. 



Only the metals of the alkalies yield principal series, and this part 

 of the paper will deal almost wholly with these principal series. It is 

 probable that the strongest lines of the calcium group, and the very 

 strong doublets in the spectra of the copper group, belong to the 

 principal series. 



The Formulae which have been Applied to Harmonic Series. 



Balmer was the first to give a formula for the harmonic series of 

 lines in the spectrum of hydrogen.* His formula is : — 



Eydberg gavef a general formula, applicable to all these series : 

 -„ where n = 10 s A. -1 ; n x and p are constants for each 



No 



00 (m + /x) 



series. N is a constant common to all series, and m = 1, 2, 3... 

 Kayser and Bunge have given the formula — 



10 s X- 1 = A - B?i- 2 - Cn~\ 



where n = 3, 4, 5... and A, B, C are constants in each series. The 

 constants B and C apply generally to the subordinate series of monad 



* ' Wied. Ann.,' vol. 25, pp. 80-87, 1885. 

 f Loc. cit. 



VOL LXX. C 



