Another interesting mental picture is drawn by Professor Herbert Wildon Carr to illustrate the philosophical meaning of the principle of relativity. Suppose that on a very frosty morning we were to see a watery vapor in the air we breathe condense into a little cloud and after floating around a while gradually disappear and become reabsorbed in the atmosphere. Assume that at the moment of this reabsorption we should undergo an instantaneous transformation of all our proportions so that our new dimensions become infinitesimal in comparison with our former state. Do you think that we would recognize the fact that we had changed? The theory of relativity declares that we would not know what had happened, because with the alteration in proportions the ratios would remain constant. The change would express itself in the new dimensions of objects around us. The little globules of water composing the little cloud would now appear like stars and planets occupying immense areas in distant spaces, far apart from each other, and all undergoing a slow age-long evolution. Such a change would be signalized as a new time and a new space. Yet the principle of relativity does not appear to our physical senses to represent a truth of nature. It is noteworthy that the principle of relativity is usually invoked when conditions are unstable, when thought is confused, and when a period of readjustment is in progress. Thus the Einstein theory may be representative of present-day harmonies, but yet may prove, in the future, to have been merely a passing philosophic mood. Bagehot, a shrewd observer, writing in 1868 about the changes wrought by Darwin's evolutionary theory, said: "There is scarcely a department of science or art which is the same, or at all the same, as it was fifty years ago. A new world of inventions has grown up around us which we cannot help seeing; a new world of ideas is in the air, and affects us though we do not see it." Those were very true words more than half a century ago, yet they serve to describe present conditions! GENERAL INDEX A, vowel sound, record of, iv, 234 Aard-vark, xii, 281-2 Abacus, or calculating machines, xv, 183-4, xvi, 61 Abalones, xii, 71 Abbe, Prof. Cleveland, i, 216-17 Abbot, Dr., solar studies, ii, 171, 186-7 Abdomen, blood circulation in, ix, 196, 197; methods of examination, x, 147, 371; muscles of, ix, 77 Abdominal Organs, control of circulation of, ix, 215, 216, 217, 220; development of, in black and white races, xv, 50; mesentery support of, ix, 59; smooth muscles in, 160-1 Aberration of Light, ii, 91-2 Abert, Lake, Oregon, xiv, 203 Abnormal Complexes, x, 355-6 Absaroka Range, xiv, 104-5, 226 Abscesses, cause (germs) of, x, 195, 198, 221; cure of neurasthenic, 58-9 Absinthe, source, xiii, 266 Absolute, technical meaning, iv, 381