The Atomic Weight of Copper

WITH reference to the Research item in NATURE of April 27, p. 660, that Messrs. Richards and Phillips have recently found the atomic weight of copper to be 63.557 (Ag = 107.88), it may be interesting to note that the spectroscopic value given in my “Analysis of Spectra” (p. 127) is 63.5569 ± 0.060, the 0.06 referring to maximum possible errors. The probable error is much less. The value obtained on spectroscopic data depends on the doublet separation and the p(1) term. These are known with very great accuracy in both silver and copper.