EFFECT OF PEESSUKE UPON ARC SPECTRA. 



219 



Second Subordinate Series : the triplet a, c, d, that is dissipated, belonging to the First 

 Subordinate Series, and the pair I, o, showing a gradual loss of intensity, belonging to 

 the Second Subordinate Series. 



Table VI. gives those lines that are strengthened and weakened under different 

 pressures. With the exception of the lines a and d of the First Subordinate Series 

 the rule holds that the nebulous lines are strengthened and the sharp ones weakened 

 under pressure. 



TABLE VI. 



N = nebulous ; S = sharp ; st = strengthened ; vv = weakened. 



c and d have the appearance of a sharp superposed upon a nebulous line at 

 atmospheric pressure, they are merged together at higher pressures, and finally vanish 

 together. 



There is no sign whatever on any of the plates under pressure of the lines given by 

 BAXENDALL! as enhanced at 454510 and 45 56 '10. 



8. SERIES OP LINES IN THE COPPER SPECTRUM. 



KAYSER and RUNGE,} who investigated the frequency relationships between the 

 lines of the copper arc spectrum, besides finding several pairs with constant frequency 



* Due to impurities (?). Not given by KAYSER and RUNGE. 



t Publications of Solar Physics Committee, 'Tables of Wave-lengths of Enhanced Lines,' 1906. 

 | KAYSER and RUNGE, ' Uber die Spectren der Elements,' 5, pp. 8-17. 



2 F 2 



