FOR KIRCHHOFF’S SPECTRAL LINES. 
109 
These values of the wave-lengths are, I trust, worthy of confidence. They may be 
liable to errors of 20 or perhaps 30 in the last figures, but, I think, to no greater error. 
A very elaborate investigation of the values of Wave-lengths of the Spectral Lines of 
the Elements has been published by Dr. Wolcott Gibbs, in the American Journal of 
Science and Arts, vol. xlvii. The basis upon which Dr. Gibbs proceeds is not the same 
° 
as mine (for instance, in the relative merit attached to Angstrom and Ditscheiner) ; 
some measures by Huggins and Van der Willingen are employed, and some new lines 
introduced ; and the fundamental treatment is different. The results, therefore, are not 
identical with mine. But, as far as I have examined, the differences between Dr. Gibbs’s 
numbers and my own are small ; not greater, I think, than can be explained by such 
errors as I have specified in the last paragraph. 
I have not yet succeeded in finding any relation between the values of wave-length 
for different lines of the same element, which can suggest any mechanical explanation 
of their origin. 
