PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 625 



another will want a temperature of 75° or eveu 80° ; this discrep- 

 ancy can be accounted for, to some extent, by the physical consti- 

 tution of the individual ; but the essentfal cause is that the com- 

 mon thermometer does not trul}' indicate the temperature which 

 we feel, but simply the temperature of the air in Avhich the ther- 

 mometer is placed ; a thermometer, to indicate sensil)le tempera- 

 ture, must have its bulb covered with a thin wet envelope. This 

 moist covering acts for the thermometer as the skin does for the 

 body, that is, cools it by allowing evaporation to take place. 



The human body itself is very uniform in its temperature ; it 

 rarely varies two degrees either way from ninety-eight degrees ; 

 five or six degrees variation beinis said to ])e fatal. 



Food, clothing, and the general temperature of our surround- 

 ings, together tend to elevate the temperature, while radiation and 

 perspiration are the chief means by which the temiDcrature is kept 

 down. 



TjMidall has shown by direct experiment that dry air docs not 

 check radiation, while moist does in a very marked degree ; dry 

 air tends to excessive insensible perspiration, while moist air regu- 

 lates it ; hence, as radiation and perspiration are cooling processes, 

 and as both take place much more rapidly in dry than in moist 

 air, the human body must of necessity lose heat more rapidly in 

 dry than in moist air. It is from this cause that a person may 

 feel comfortably warm in the moist atmosphere of a temperature 

 which would be from 7 to 10° too cold if the same was dry. 



From the al)ove, we may infer that considerable saving in fuel 

 may be etfected by keeping the air in a healthy moist state. The 

 mean temperature for the cold months is as follows : November, 

 40.40°; December, 30.58° ; January, 27.03°; February, 27.61° ; 

 March, 35.52° ; mean of the whole, 32.23°. 



The cost of warming must depend directly upon the number of 

 degrees through which it is necessary to raise the temperature of 

 the air. If we permit the air of our sitting rooms to become very 

 dry, we must maintain a temperature of say 72° to be warm, Avhile 

 in moist air 65° would be warm enough ; in one case we warm the 

 air 40° (from 32° to 72°), while in the other we have to warm it 

 but 33° (from 32° to 65°) ; that is, make a saving in fuel in the 

 proportion of 32 to 40, or of nearly 20 per cent. 



The practical utility of the hygi^odeik may be thus briefly stated : 



It is a guide which, if followed, will enable us to maintain an 

 atmosphere in inhabited rooms of such a nature — 

 [Am. Inst.] NN 



