4S 



THE AMERICAN BEE-KEEPER. 



March, 



therefore, of loss and gain through 

 radiation is a hirger loss in cold weath- 

 er than in warm. 



The rate of loss of heat by con- 

 duction depends upon the nature of the 

 conducting body and upon its tempera- 

 ture. The lower its temperature the 

 faster any conductor will carry away 

 the heat of a warmer body with which 

 it is in contact. There are lar.ye < 

 ferences in conductivity of different 

 substances. In winter bees are gen- 

 erally in contact only with the combs 

 on which they cluster and the air 

 which surrounds them. Beeswax is a 

 poor conductor of heat, and for that 

 reason makes an excellent resting 

 place for bees in cold weather. If the 

 combs were made of metal it would 

 draw off the body heat of the bees so 

 rapidly that they probably could not 

 withstand low temperature, though 

 well sheltered. Dry air is a rela- 

 tively poor conductor of heat and 

 as long as the air in the hive 

 is dry and somewhat stagnant, 

 large clusters of bees with plenty 

 of food can withstand very cold 

 weather. The conductivity of dry air, 

 ■water, and silver are to each other 

 respectively, as 1:25:19571. The con- 

 ductivity of moist air seems not to 

 have been accurately determined. The 

 only statement the writer can ifinjd 

 concerning its value is, that one in- 

 vestigator found that of .steam to be 

 higher than that of dry air. It is, 

 however, a matter of common experi- 

 ence that in damp, foggy or rainy 

 winter weather one is colder than on 

 dry days, with the same temperature. 

 This has been explained by excellent 

 scientists as being due to the superior 

 conducting power of water vapor in 

 the air and in one's clothing. This 

 seems reasonable though it is not a 

 matter of course. Moist air is not nec- 

 essarily dry air and water. It may 

 be, and more often than otherwise Is, 

 dry air and vapor. 



Water vapor is one of th^ several in- 

 visible ga^ses of which the atmosphere 

 is composed, and it is always present 

 in the driest weather and in the most 

 arid regions. Its chief difference of 

 behavior from the other gases is that 

 it becomes liquid at a considerably 

 higher temperature than they do. It is 

 produced by evaporation from water 

 and ice at all temperatures, slowly 

 at low temperatures, fa-ster at high 

 temperatures. 



There is a definite amount of water 

 rapor which can exist in the air at any 

 moment, and this amount depends 

 mainly upon the temperature. The 



higher the temperatvire the larger the 

 quantity of vapor possible. For ex- 

 ample, the maximum amount at 32 de- 

 grees Fahr. is 2.113 grains per cubic 

 foot, at 110 degrees is 26.112 grains. 

 When this limit is reached the vapor 

 is said to be saturated, and any further 

 addition of vapor results in changing 

 some of it by condensation into water. 

 If there is less than the maximum 

 amount of vapor that can exist in the 

 air at any moment, the degree of sat- 

 uration is expressed in percentage, and 

 this is called the relative humidity. 

 For example, a relative humidity of " 

 per cent •signifies that there is iu the 

 air 3-4 of the total amount that can ex- 

 ist at that temperatiu-e. Since the 

 possible amount of vapor decreases 

 with the temperature, any sudden cool- 

 ing of the air increases its relative hu-. 

 midity. If, for example, the air at 

 45 degrees with a relative hiimidity ol 

 75 per cent were cooled to 37 degrees, 

 the vapor would be more than saturat-! 

 ed and some of it turned to water. 



If water vapor is a better conductoi 

 of heat than dry air, its conductivitj I 

 must increase with the relative hu: 

 midity: i. e., the nearer it approaches.' 

 saturation. When condensed int( 

 water it is twenty-^five-fold a , bette?,' 

 conductor of heat than dry air, as w« 

 have seen. 



Cellars are frequently bo damp t" 

 at moderate temperatures, the air ii 

 nearly saturated and small reduction 

 of temperatiu'e bring about condensa 

 tion. The normal .Tanuary tempera 

 ture of Boston, Mass.. is 27 degrees 

 and the normal relative humidity 73.1 

 per cent. At this time of year in thai 

 region the average temperature of i 

 tolerably tight cellar might be 40 de 

 grees with an average relative humid 

 ity of 85 per cent to 90 per cent. (Thi 

 writer has just measured the condi 

 tions in his house-cellar, and find-s th' 

 temperature to be 41 degrees, the rel 

 ative humidity 92 per cent, and th 

 dew point 40 degrees. That is to say 

 if the temperature should fall one de 

 gree, dew would form in the cellar. 

 The humidity of course depends Tipoi 

 its ventilatiou; but in cold location 

 in order to keep cellars from freezini 

 it is necessary to make them so tigh 

 that the ventilation is poor. With ai 

 average cellar temperature of 40 d€ 

 grees and a relative humidity of 8 

 per cent to 90 per cent, the air in 

 side the hive, owing to the moisture ex 

 haled by the bees, would lively be 9 

 per cent snturated and upwards. Th 

 writer has no observations of hive ten: 

 peraturos in winter, but assuming i 



