a newspaper notice which might give much pleasure or pain to a man in private life. Such facts must be taken into account by any economic theory which seeks to determine the best distribution of wealth. The relation between the duration and intensity of pleasures and pains seems to be of special importance. Supposing the intensity to remain the same, the amount of pleasure is directly measured by the time it lasts. Pleasures from disparate sources, e.g., eating one's dinner comfortably at home or going out to a concert, may be more or less exactly compared by noticing which is habitually chosen. We can further (as is done in physics) define intensity in terms of time. If a pleasure (e.g., eating a pear) last half as long as another (e.g., eating two apples), and yet the two pleasures be regarded as equal (e.g., to a child having five cents to spend and being in doubt whether to buy one pear or two apples) the former pleasure may be regarded as having double the intensity of the latter. Pleasures and pains are also correlated, as when one decides to attend an opera, knowing it will be followed by headache. Money spent in the purchase of pleasures lasting equal or commensurable times, measures roughly the intensity of pleasure, and (when money must be obtained by painful labor) correlates pleasures and pains.
19. Extensity, if it be a mental magnitude, is still more obscure than intensity.
It has been recently urged[1] with much force, that sensations must have a quality corresponding to the size of external stimuli. Attempts to explain the perception of space apart from such a quality in sensations, certainly seem unsuccessful. In any case there is a threshold of size as there is a threshold of time and intensity of stimulation. The area must be increased as the time and intensity are decreased, and the quantitive relations may be determined by experiment. Such determinations may also be made for sensation-areas on the
- ↑ By Prof. Stumpf in Germany, Prof. James in America, and Dr. Ward in England.
