expected, as we know that the lower animals easily learn to understand spoken words. CORRESPONDENCE. _COMPARATIVE LONGEVITY AND GREATNESS._ Whether or not great men are favored by an increase of years above those allotted to more ordinary mortals has long been a question of interest, and has acquired a special importance in connection with the study of the natural history of men of genius, and the discussions of the possible relation of greatness to degeneracy and to insanity. Questions of this type can only be decided on the basis of extensive and carefully collected data, which unfortunately it is difficult and at times impossible to collect or to find. It is therefore natural that such evidence as seems to exist and to carry with it some degree of logical force should be brought forward in proof of a claim which on general principles is both pleasing and plausible. Of this type is the problem of the relation between longevity and greatness, and of this type is the evidence now and then brought forward to substantiate the belief that great men are, as regards longevity, an unusually favored class. The most recent presentation of the topic (by Mr. Thayer in the Forum, February, 1900) collects a list of some five hundred prominent men and women of the nineteenth century and finds that these persons lived on an average sixty-eight years and eight months; that is, nearly thirty years longer than the population as a whole. And on the basis of this conclusion the writer combats the notion that nineteenth-century men of genius or of eminence exhibit signs of degeneracy, because longevity and the ability to do sustained work for a large number of years is in itself a sign of unusual vitality and vigor. As these conclusions are apt to be extensively quoted, and as they seem to me founded upon a serious fallacy, I shall attempt to present as simply as possible the nature of the desired evidence which alone could prove that great men are longer lived than others, and to show that the evidence thus far presented is inadequate to support the conclusion which has been drawn. Mr. Thayer is not the first one to present the average age at death of a number of eminent persons as evidence of unusual longevity. In an article which was reprinted in the Popular Science Monthly for May, 1884, the average age at death of 1,741 astronomers was given, and found to be sixty-four years and three months; and on the basis of this fact the author claimed that astronomers enjoyed unusual longevity. In a brief contribution published in Science, October 1, 1886 (and republished in Nature, November 4, 1886), I called attention to the fallacy inherent in such conclusions, and also presented some new contributions to the question of the longevity of great men. The materials of that article I shall utilize in the present discussion.