36 The Ottawa Naturalist. [May 



heat on persons in the room. Let us note the difference! It 

 will not have occurred to many of us to enquire just how it is 

 that we are warmed by heat, and more will be surprised when I 

 say we are ordinarily not warmed by a furnace, but are only 

 kept from getting cold or chilled. How, I am asked? We shall 

 see. As all know, our bodies in health are maintained at a 

 temperature of 98.4 F., some 30 degrees higher than the or- 

 dinary air of the room, so that clearly the air of the room cools 

 us by^ abstracting heat from us, rather than by warming us. 

 But we know that we have no sensation of cold and are warm; 

 which simply means that we have not lost our body heat to the 

 air of the room , so fast as to give us a sensation of cold. This 

 is due to the non-conducting clothing which we wear and to the 

 enveloping air being not too heated or too cold. 



It is, however, quite manifest that wdiat too hot or too cohf 

 means depends directly, other things .l;eing equal, upon the 

 amount of fuel and upon the free circulation of the results of 

 vital combustion in the human organism. The old person, the 

 anaemic person, the person with poor circulation will be cold when 

 the healthy are warm and so such must put more clothingon. But. 

 moreover, there are in the air of the room say at from 60° to 70'^ F. 

 some other differences depending upon the kind of indoor heating 

 so great as to create very material differences in the effect of air 

 at different temperatures upon the same person. I would recall 

 to you the .three ways by which all bodies lo.se their heat: (a), 

 by radiation, (b) by conduction, (r) by evaporation. If we 

 sit in front of a grate fire the air between the fire and us ma\- he 

 no higher than 7.0° F., but the side of our face towards the fire 

 may actually be over 100° F. This is due to radiation and 

 means that heat waves 'penetrate into the tissues and warm the 

 body, penetrating indeed deeper than the skin as well as into the 

 walls opposite the fire. The same result, but less apparent, is 

 obtained by the radiation from hot-water pipes, while in ad- 

 dition these warm the air in contact with them and this, ascend-. ' 

 ing, again warms, the particles of air it comes in contact with bv^ 

 convection. Now it will be apparent that if air comes into a 

 room from a hot-air furnace, it in no wav fulfils the first principle 

 of heating by radiation; hence, it is found by experience that 

 the air of a room at 60° F. receiving radiant heat from a radiator 

 often gives a sensation of comfort as great as hot-air at 70° to 75°. 

 There is, however, another equally important cause affecting the 

 loss of body heat, viz., degree of moisture in a room or its relative 

 humidity. You will remetnber I' spoke of the fact last vear 

 that air at 0° F. holds less than 1 grain of water vapour and "that 

 with every 20 degrees increase, say, to 70°, such increase of its. 



