Preston— Radiation Phenomena in a Strong Magnetic Field. 387 
At length, by pushing the pole pieces of the magnet quite close together, 
so as to Jeave only a small space for a very small spark between them, I was 
able to so inerease the strength of the magnetic field around the source of 
light that I not only obtained pronounced broadening, but, on further careful 
adjustment, I was able to completely separate the components in the case of 
certain lines and photograph the modified line as a distinct triplet. 
Typical of this class of lines are the lines 4678 and 4680 of cadmium 
and zine. These lines are in the violet end of the spectrum, near the 
blue, and are not to be confounded (as to the effect exhibited) with the blue 
cadmium line of 4800, or the D lines of sodium, which appear to be the lines 
investigated by Zeeman and other observers. As to the distinction between the 
classes of effect as exhibited by the appearance of the modified lines, I shall speak 
more fully in the sequel; at present it is sufficient to state that, although some 
become resolved into distinct triplets, others photograph as doublets (the light 
being viewed across the lines of force), or weak-middled, greatly broadened lines, 
having the appearance of quartets; while, on the other hand, many lines appear 
to be simply broadened in the same magnetic field, and others seem to be scarcely 
influenced in the same magnetic field. 
It is clear, therefore, that the magnetic effect depends not so much on the 
wave-length of the spectral line as on some hidden quality which we may refer to 
as the character of the line; for lines of nearly the same wave-length, even of the 
same substance, show effects which differ remarkably in magnitude and character. 
Such laws, therefore, as that the broadening of the spectral lines is proportional 
to the wave-length, or to the square of the wave-length are shown to be utterly 
untenable, unless, perhaps, it might be possible to group the spectral lines of each 
substance into sets, so that some law of wave-length might apply to the lines of 
each set. 
For the purpose of investigating this important point, more especially as 
certain limited groupings of the spectral lines have already been made, it became 
clear that a stronger magnetic field would be a matter of the highest importance. 
I consequently determined to have an electro-magnet built according to a special 
design, with the hope of producing an intense magnetic field in the region occupied 
by the source of light. While this instrument is being constructed I have been 
able to obtain the use of a large U-shaped electro-magnet, which gives me a 
considerably stronger field than that which I at first employed. For the use of 
this instrument I am indebted to the great kindness of the Right Rey. Monsignor 
Molloy. 
With it I have been able to work up the magnetic field to such a strength (by 
bringing the pole-pieces very close together and using a very small spark) that 
the photographs display the triplets of the zinc and cadmium lines 4680 and 
3M2 
