64 REPORT—1899. 
Science Association. Subsequently the quartet form (which we have now 
proved in the cases observed to be really a sextet) was independently 
observed by M. Cornu! and others. 
3. Finally, from the various observations of the character and measure- 
ments of the amount of the magnetic effect experienced by the various 
spectral lines of several substances, a general law has been inferred con- 
cerning the effect which may be stated as follows : >— 
(i) The spectral lines of a given substance may be divided into groups 
such that all the members of one group suffer the same kind of perturba- 
tion in the magnetic field, but the kind of perturbation of all the members 
of another group is different. Thus, for example, in the series of triplets 
of zine, the first of one triplet is similarly affected to the first of each of 
the other triplets, while the second of one triplet is affected in the same 
way as the second in each of the other triplets, but in a different way from 
first and third of the triplet. Hence the series of firsts of each triplet 
constitute a group all the members of which are similarly affected, and the 
series of seconds and thirds are other such groups. 
(2) The character of the effect is the same in the corresponding lines 
of the spectra of chemically related elements. Thus, the triplets of cad- 
mium are affected in the same way, both as regards the character and the 
magnitude of the effect, as are the triplets of zinc. 
(3) If the magnitude of the effect be measured by the difference of 
wave-length of the lateral components of the magnetically resolved line, 
then throughout any one group the magnitude of the effect is inversely 
as the square of the wave-length of the line. This means that e/m is 
the same for all the lines of the same group, but not the same for all the 
lines of the spectrum. In other words, the difference of frequency 
between the lateral components of the magnetically resolved line is the 
same for all the lines of the same group ; and if the magnitude of the 
effect be measured by this difference of frequency, then we may say that 
the effect is the same in character and magnitude for all the lines of the 
same group. It differs from group to group in any one substance, but is 
the same for corresponding groups in different substances. 
Further information will be found in this connection in the ‘ Philo- 
sophical Magazine,’ vol. xlvii. p. 165, February 1899, and the ‘ Phil. Trans. 
Royal Dublin Society,’ vol. vi. series IT. p. 7, 1899. 
Determining Magnetic Force at Sea.—Report of the Committee, con~ 
sisting of Professor A. W. RtcKer (Chairman), Dr. C. H. Lrxs, 
(Secretary), Lord Ketvin, Professor A. ScutusTER, Captain E. W. 
Creak, Professor W. Stroup, Mr. C. V. Boys, and Mr. W. 
Watson, appointed to investigate the Method of determining Mag- 
netic Lorce at Sea. 
Some information has been collected as to the methods used at sea by 
different countries, and Captain Creak has carried out experiments at 
Kew by Lloyd’s method with encouraging results. 
1 Comptes Rendus, 1898, 126, p. 181 and p. 300. 
2 his law was published in Waturv, lix, 248, January 12, 1899. 
