Microscope Spectrum Apparatus. Bij IT. C. Sorby. 205 
developed. All these facts will be more easily understood by means 
of Fig. 4. 
■p[G. 4. SPECTKA OP OORHODE1NE DISSOLVED IN ABSOLUTE ALCOHOL. 
700 bed 400 
Strongly acid . . 
Very slightly acid, 
or neutral 
d ’} 
a b cl 
x] y z 
On discussing the wave-lengths of the centre of the bands in 
the case of the neutral solution I have found that they constitute 
two different series of three bands each, having the central band in 
common, those in each of the two series having the same interval 
ratio, but the intervals between the two series different, and related 
to one another in some such ratio as 5 to 8. Perhaps my meaning 
will he more easily understood by representing the wave-lengths by 
letters, and the relative ratios of the intervals by numbers, as 
follows : 
! 5 5 
Neutral j a Ij 0 
1 
Strongly acid 
It will thus be seen that a strong acid entirely destroys the series 
at the wider interval (x y z), removes the band ( a ) at the red end of 
the narrower series (a b c ), and develops the new band ( d ) at an 
equal interval towards the blue end. 
I could give many other illustrations of similar facts, but these 
few will, I trust, suffice to show that this wave-length method of 
study enables us to establish simple relations in cases where little 
or no connection could be recognized if any arbitrary scale were 
adopted, and such being the case I do not hesitate to claim for 
it precedence of all others. 
5. Relation between the Bands in different closely connected 
Compounds. 
So far I have considered only cases where a substance is examined 
merely in different physical states, but now proceed to those in 
which the physical state is the same , but the substance itself 
j b c d 
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