560 CRITICAL NOTICES: perienced " (p. 54). Introspection teaches us that sensations differ in intensive chararacter, not in intensive quantity (p. 56, footnote). Quantity, both as regards extent and as regards intensity, is an effect of psychic synthesis, formed on the basis of the qualitative differences in extensity and intensity possessed by sensations (p. 62). Hence from the psychological standpoint sensations are with- out magnitude and are consequently immeasurable. For any mag- nitude is only measurable so far as it can be conceived as composed of equal parts (p. 53). But every sensory experience, whether it be a sensation or a difference of sensations is indivisible, except by reference to the object of experience. We can only form an estimate of the intensity of a sensation or of a sensation difference by passing from the sensation or sensation difference itself the domain of psychology to external objects, the domain of physics (p. 91). " The psychic phenomenon ... is limited to that which, appears subjectively to us. What can exist independently of ourselves is the physical fact " (p. 76). Thus we reach the con- clusion that the measurements resulting from the methods of experimental psychology, do not determine the quantity of psychic phenomena ; they merely serve " to fix the qualitative variations objectively " (p. 244). Prof. Aliotta's work will well repay a careful reading. It is written in a lucid, methodical manner and contains indisputable truths which at least in the past reign of crude psycho-physics, have been too often neglected. Nevertheless, it seems to me that the discovery to which the above premisses have brought him is- very like, if indeed it be not actually, a mare's nest. Surely all modern psychologists will admit at the outset that a sensation or a sensation difference, taken by itself, is devoid of magnitude. But must they therefore follow Prof. Aliotta and assert that two sensations cannot be directly compared ? " Taken by themselves," he says, "two different brightnesses can only be considered as equal or unequal." A judgment of their greater or less intensity, he maintains, is only possible by taking into consideration their respective distances from a third brightness which is chosen as the point of reference in the qualitative series (p. 66). Unquestion- ably there is confusion here between appreciation of direction of difference, on the one hand, and mathematical measurement, on the other. We are surely justified alike from the standpoint of experience and on histological grounds, in conceding the psycho- logical faculty of observing the nature of the difference between two sensory experiences. While it is one thing to admit that we can appreciate the equality or difference of two sensations (or of two sensation differ- ences), it is of course quite another to urge that sensations (or sensation differences) are of measurable magnitude. With Prof. Aliotta's denial of the latter statement I am in entire agreement. I take exception, however, to one, at least, of the arguments by which he seeks to maintain his position. He brings forward the
