KATA THERMOMETER. In considering measurement of ventilation we must bear in mind that the ordinary thermometer merely gives the average temperature of its surroundings. While the human body produces heat, and all day long is keeping itself at body temperature, the thermometer does not produce heat, but just registers the effect of the surrounding atmosphere upon itself. An instrument is needed, therefore, to indicate the cooling and evaporating power of the air.
The Kata thermometer is such and is far more indicative of human feeling than the ordinary thermometer. It records not only the effect of the temperature of the surrounding air on the cooling of its surface when at body temperature, but of the wind and any movement of the air, and also how quickly cooling takes place when its surface is wet, as the skin is when perspiration is going on. The Kata thermometer is a large-bulbed alcohol ther mometer of standard size with stem graduated from 100° to Fahrenheit. It is warmed up in hot water till the meniscus rises above 100° F, the bulb is then dried, and the rate of cooling of the meniscus from 100° to 95° F taken with a stop-watch. From a factor number determined for each instrument, the cool ing power is deduced in millicalories gramme calorie) per sq.cm. of the surface of the bulb at body temperature per second.
In still air the dry Kata thermometer has a cooling power of about 10 at o° C, and about 5 at 2o° C; with a wind of 9m. per hour it has a cooling power of about 4o at o° C, and 20 at about 15° or 16° C, and so on with different rates of wind. Wind is far more important than temperature to the cooling of the body ; thus the still air is easily borne. In the case of the wet Kata thermometer a wet muslin glove covers the bulb. In factories, schools, etc., the reading of the cooling power of the dry Kata thermometer should not be less than 5-6 with a temperature of about 6o° F, 7 at 7o and 8 at 8o°, otherwise the efficiency of the worker and pupil will tend to go down. Observations made by the Industrial Fatigue Board in pottery, boot and shoe, cotton and printing works, showed that a great number of readings were below 6. The general mortality is greater in the trades with the lower readings. Great improvements could yet be made in this respect. See Medical Research Council, Special Report, No.
73 (1923). (L. E. H.)