Page:Popular Science Monthly Volume 65.djvu/151

Mendenhall the analogous conception of word-spectra or characteristic curves. Just as the light-rays of various wave-lengths emitted by a substance combine to form its spectrum, so a combination of words of various lengths in proper definite ratios make up an author's word-spectrum or characteristic curve. The analogy is imperfect, but we admit it. But is it true that each substance has a single spectrum? This was the supposition when the science of spectrum analysis was in its infancy, and upon this supposition Dr. Mendenhall bases his analogy. The fact is that over forty years ago it was demonstrated that some substances have several spectra, and to-day it is generally believed that all substances have several spectra, corresponding to the several stages of disassociation or molecular composition of their molecules. The analogy to spectrum analysis, therefore, demands the modification of the theory of characteristic curves, which I have tried to point out in the preceding pages.