/ 
138 Harriry—An Investigation of the Connexion between Band and Line Spectra. 
In the absence of any positive proof of the dissociation of the atom, and the 
proof that highly endothermic reactions take * place between reacting substances 
in the oxyhydrogen flame, which are not accomplished by heat alone, and are 
therefore the result of an exalted chemical activity of the reacting substance, 
I conclude that the metallic elements with monatonie molecules which exhibit two spectra, 
one of lines and the other of bands, can exist in two different conditions, the difference 
being in the larger amount of energy associated with the atom which exhibits a line spectrum. 
The acquisition of energy by the primitive or normal atom arises from tts chemical properties, 
and from the excess of energy transferred to vt in the flame, or arc, over that which is 
necessary to liberate the atom from its compounds. 
Note ON THE ILLUSTRATIONS. 
The figures above the photographs give an approximate seale of wave-lengths. 
The two yellow sodium lines are indicated by the symbol Na, the mean of their 
wayve-leneths being 5893. The number 6000 is at a little to the left of this. 
The number 3000 represents a wave-length lying just beyond the edge of the 
photograph. 
On Plate I. the ultimate line in the spectrum of silver is shown as lying 
between 3500 and 3000. It is the least refrangible of the two lines that remain 
after the composite bands in which they oceur have become extinct. 
The figures in brackets after the name of the metal serve to identify the 
photographie plate from which the spectra were copied. 
In one or two instances the description in the text may not exactly tally 
with the reproduction. On Plate II., for example, some lines are absent from 
the weaker spectra which are plainly visible on the silver prints from the same 
negative. 
In the spectra of rubidium, cesium, and thallium, it will be observed that 
in each case where there is a pair of lines, it is the more refrangible of the two 
which is the stronger, and which remains after the other has become extinct. 
* «On the Thermo-Chemistry of Flame-Spectra at High Temperatures.’’—Proc. Roy. Soc., A, 79, 
pp. 242-261. 1907, See Part III., pp. 253-261. 
