In order to connect the readings of this device with human sensations, Hill and his collaborators have used the instrument under a great variety of atmospheric conditions, both indoors and out, and compared the readings with independent estimates of comfort and discomfort. On an ideal summer day the “wet kata” fell from 110 to 100 in 25 seconds, and the “dry kata” in 85 seconds. Indoors at the seaside in summer, under comfortable conditions, the readings were 50 seconds and 140 seconds, respectively. A large number of other readings, taken under different conditions in various parts of the word, have been published. The katathermometer is now used in both Great Britain and the United States in the study of ventilation problems, and has acquired a rather extensive literature. According to its inventor, “the heating and ventilation of rooms should be arranged so that the wet-bulb falls from 100 to 90 degrees in about one minute, and the dry-bulb in about three minutes.” [Illustration: A WEATHER BUREAU KIOSK, IN UNION SQUARE, SAN FRANCISCO. (_Photograph, U. S. Weather Bureau._)] [Illustration: THE UNITED STATES WEATHER BUREAU STATION, OBSERVATORY TYPE, AT PEORIA, ILLINOIS. (_Photograph, U. S. Weather Bureau._)] Regardless of the merits of these particular instruments, it is certain that the cooling power of the air--which is quite a different thing from the temperature of the air--is a very important factor in determining our comfort and our health. Within certain limits the body can easily adjust itself to changes in the cooling power of the air; within wider limits the adjustment is effected with difficulty, and we experience discomfort and possibly suffer in health; and finally there are extreme conditions, in either direction, to which adjustment is not possible; the internal temperature is then either lowered or raised, as the case may be, and a comparatively small change of this sort is fatal; i. e., death results by chilling or by heat stroke. [Illustration: Photo U. S. Weather Bureau THE CENTRAL OFFICE OF THE UNITED STATES WEATHER BUREAU IN WASHINGTON]