714 
CHEMISTRY: HARKINS AND ARONBERG 
may be seen that these changes of voltage and amperage produced on 
noticeable changes in the shift of the lines. Finally, to estabhsh the 
change in a new manner, the uranio-lead was removed from its lamp, 
and ordinary lead put in its place, and when this was done the shift was 
found to disappear. 
When Merton did his work on the isotopes of lead, J. W. Nicholson 
calculated for him the shift in a lead Hne at X = 4000, which would be 
caused by an atomic weight difference of 0.5 unit according to Professor 
Hicks' theory that the atomic weight term enters exactly into the sepa- 
ration of doublets and triplets in series spectra, and assuming that at 
this wave length lead has a doublet series spectrum with a separation 
of 50 A. U. The calculation showed that the shift should be 0.15 ang- 
stroms which is very much larger than the shift actually found. On 
the other hand the theoretical formula developed by Bohr 
gives a much smaller value (0.00005 angstroms) but of the same sign as 
that found experimentally. However, Bohr's calculation was made for 
an extremely simple atomic system, while the lead atom contains a 
large number of non-nuclear electrons (probably about 82). 
Since this is the first investigation reported in which a shift has been 
found in the spectra of isotopes it would seem advisable to check the 
experimental work by an altogether new investigation, especially since 
the shift as determined is extremely small. However, it should be 
stated that|the difference in the position of the lines is easily observable 
under the measuring microscope. One remarkable feature of the photo- 
graphs is that the lines seem to be shifted, and not to be broadened. 
We wish to thank Prof. H. G. Gale for directing the spectroscopic 
work and Prof. Theodore W. Richards for the extremely rare Radium 
G which he placed at our disposal for this work. 
iBohr, Phil. Mag., London, 26, 1913, (1, 476, 857); 29, 1915, (332). 
2 Russell and Rossi, London, Proc. R. Soc. (A), 87, 1912, (478). 
^Berlin, SitzBer. Ak. Wiss. 121, Ila, 1912, (175). 
4 Trans. Chem. Soc, 105, 1914, (140). 
5/. Amer. Chem. Soc, Easton, Pa., 38, 1914, (1329). 
^Phil. Mag., London, 27 y 1914, (854-68). 
T Berlin, SitzBer. Ak. Wiss. 123, Ila, 1914. 
^London, Proc. R. Soc. (A), 91, 1914, (198). 
