of simple mental processes of which Ernst Heinrich Weber set the fashion some forty years ago, and the necessity of extending which in every possible direction becomes more and more apparent to students of the mind.  Think of making forty thousand estimates of which is the heavier of two weights, or seventy thousand answers as to whether your skin is touched at two points or at one, and then tabulating and mathematically discussing your results!  Insight is to be gained at no less price than this.  The new sort of study of the mind bears the same relation to the older psychology that the microscopic anatomy of the body does to the anatomy of its visible form, and the one will undoubtedly be as fruitful and as indispensable as the other.

Dr. Ebbinghaus[1] makes an original addition to heroic psychological literature in the little work whose title we have given.  For more than two years he has apparently spent a considerable time each day in committing to memory sets of meaningless syllables, and trying to trace numerically the laws according to which they were retained or forgotten.  Most of his results, we are sorry to say, add nothing to our gross experience of the matter.  Here, as in the case of the saints, heroism seems to be its own reward.  But the incidental results are usually the most pregnant in this department; and two of those which Dr. Ebbinghaus has reached seems to us to amply justify his pains.  The first is, that, in forgetting such things as these lists of syllables, the loss goes on very much more rapidly at first than later on.  He measured the loss by the number of seconds required to relearn the list after it had been once learned.  Roughly speaking, if it took a thousand seconds to learn the list, and five hundred to relearn it, the loss between the two learnings would have been one-half.  Measured in this way, full half of the forgetting seems to occur within the first half-hour, while only four-fifths is forgotten at the end of a month.  The nature of this result might have been anticipated, but hardly its numerical proportions.

   [Footnote 1:  “Ueber das Gedaechtniss.  Untersuchungen zur
   experimentellen Psychologie.”  Von Herm. 
   Ebbinghaus.  Leipzig:  Duncker u.  Humblot, 1885. 10+169 pp. 8vo.]

The other important result relates to the question whether ideas are recalled only by those that previously came immediately before them, or whether an idea can possibly recall another idea, with which it was never in immediate contact, without passing through the intermediate mental links.  The question is of theoretic importance with regard to the way in which the process of “association of ideas” must be conceived; and Dr. Ebbinghaus’ attempt is as successful as it is original, in bringing two views, which seem at first sight inaccessible to proof, to a direct practical test, and giving the victory to one of them.  His experiments conclusively show that an idea is not only “associated”