RELATIONS OF THE AIR %0 OUR CLOTHING. 657 



within a cooler atmosphere. Such bodies lose their heat in three 

 different ways: 1. Radiation. 2. Evaporation. 3. Conduction. This 

 triple arrangement is of great advantage for the heat-department of 

 our organism, inasmuch as the existence of these different routes 

 allows of a delicate regulation that, for instance, which we lose in a 

 given case by radiation can be made up by diminution of loss through 

 the other routes, and vice versa. The losses by radiation and by con- 

 duction are the most constant under equal conditions, and evaporation 

 of water is the principal means for equalizing differences resulting 

 from varying production of heat or from difficulties of the two other 

 routes. Allow me to illustrate this by drawing your attention to 

 some every-day phenomena. 



You arrive, for instance, in an hotel after a journey during a cold 

 winter's day, and have at once a fire lit in your room. Let the fire 

 be ever so bright, the thermometer even rise to a reassuring degree 

 you must stick to the fireplace ; the room does not get warm. If you 

 continue to live in the same room and have the tire kept in, it will by- 

 and-by get comfortable even if the thermometer in the room should 

 stand lower than on the first day, and you will think quite correctly 

 that the room wanted time to get warmed through and through. 

 Before that had taken place, the loss of heat by increased radiation 

 into the incompletely warmed space made itself sensibly felt in the 

 heating department of your body. Radiation is the stronger the 

 greater the difference of temperature between the two bodies. Sur- 

 rounded as you are in a room not only by air, say of 68 Fahr., but 

 also by walls, furniture, etc., which stand, perhaps, at 38 to 40, your 

 body radiates its heat particularly toward these colder objects, till 

 they also get warmer. For a room to be warm, it must get warmed 

 with all which it contains. 



Let us now look at the contrary case, when our loss by radiation 

 is uncommonly limited ; for instance, in a thronged room on a warm 

 and moist day. You feel an oppressive heat, and scarcely trust the 

 thermometer, which marks only 68, perhaps your favorite tem- 

 perature. Quite correctly, you accuse the throng of people, and 

 retire into an adjoining room, where you find the air delicious, and 

 seem to receive new life ; there, again, the thermometer is suspected 

 by you, as it is scarcely different from its colleague inside ; and if the 

 air in the two rooms were to be examined eudiometrically, the differ- 

 ence would be so small as to leave unexplained the difference in your 

 sensations. What, then, causes this difference ? It is the suppression 

 of your lateral radiation of heat, when you are in the midst of other 

 equally warm bodies ; your receipts and expenditure by radiation 

 cover each other, and the cooling of the individual limits itself to the 

 two other routes, conduction by the air moving round him, and evap- 

 oration of water from his surface. On such occasions the pores of 

 your skin pour forth a quantity of water, and, at the same time, you 

 vol. x. 42 



