Suggested by this question of “life span” of sensations is another characteristic which one might expect to find important,—viz., what we have in an early chapter referred to as the “tendency to adaptation” of the different senses. In the case of odors, temperatures, and contacts, we easily and speedily become adapted to continuous presence of impressions and cease to be aware of their existence. Thus, we soon become adapted to the presence of hats on our heads, the clothes on our backs, the smell of smoke, and even to such extreme temperatures as that of the stoking room. Continuous stimulation of one of these senses so raises the threshold of the sense organ that the original stimulus ceases to be effective. So far as practical and æsthetic purposes are concerned, we are then fatigued to the particular impression. We may be gratified to find that this tendency to adaptation is not nearly so conspicuous in the case of sight. But we will be equally dismayed to learn that the tendency is as prominent in the case of hearing as it is in the so-called lower senses. Moreover, this tendency refers to continued stimulation of the same degree or quality, whereas in æsthetic manipulation the qualities presented are varied from moment to moment and from point to point. _Spatial Attributes of Taste Qualities_ On the whole, then, these strictly psychological or psychophysical comparisons are so unsatisfactory that we are compelled to look elsewhere for the criteria of the raw material of æsthetics. Some writers have suggested that the absence of definite and formal spatial attributes and systems is what makes certain of the senses unsuitable for æsthetic treatment. But there are two important objections to this suggestion. One is our earlier question as to the reasons why æsthetic treatment should necessarily consist of arrangement in spatial and temporal series and patterns. Unless some excellent reason to the contrary is given, we are free to assume that this is not a necessity, but merely an incidental result, following from the character of the materials, which, for other reasons, for which we seek, are chosen as the raw materials for æsthetic treatment. The other objection, which is, perhaps, more convincing, is the fact that, whereas touch and kinæsthetic impressions both possess immediate voluminousness and take their place readily in a spatial manifold of position, direction, distance, and form, they do not yield to æsthetic treatment; while sound and taste, one of which easily ranks second and the other of which belongs low down in our æsthetic scale, possess extent in only a very doubtful and probably analogical manner, and are almost, if not wholly, lacking in those qualities which would enable them to participate in a manifold of position, direction, distance, and form. As for temporal attributes, such as duration and sequence, all impressions possess them, from whatever sense they originate. The idea that the difficulty or