ILLINOIS STATE BEE-KEEPERS' ASSOCIATION 



77 



Assumed cluster 

 temperatures. 



Dry 

 bulb 



60°. P. 

 60OF. 

 60°F. 

 60° P. 



Wet 

 bulb 



54°F. 

 52°F. 

 50op. 

 48° P. 



Dew 

 point 

 49°P. 

 45°P. 

 40OF. 

 35°P. 



Relative 

 humidity 



68 per cent 

 58 per cent 

 48 per cent 

 39 per cent 



With such an assumed temperature 

 of the cluster (60° P.) only the highest 

 relative humidities would show con- 

 densation in an atmosphere in which 

 such a cluster temperature would be 

 found, for such a cluster temperature 

 could occur only when the external 

 temperature is above 57°F. 



If different temperatures are as- 

 sumed for the cluster (all of which have 

 been observed under different condi- 

 tions by various investigators) the rela- 

 tive humidity of the warmer atmos- 

 phere which will show no condensation 

 when cooled to cellar temperature is 

 given in the following table (barome- 

 ter, 30 in.). 



Assumed cluster 

 temperatures. 

 Dry Wet Dew Relative 



bulb bulb point humidity 



60°P. 52°F. 45°F. 58 per cent 



65°F. 54oP. 45°P. . 48 per cent 



75op. 58. sop. 46°P. 35 per cent 



960F. 660F. 45°F. 18 per cent 



In this second table the numbers are 

 chosen so that the dew-point is prac- 

 tically\45°P. in all cases, assumed as 

 an average cellar temperature. It ap- 

 pears that a given amount of water 

 given off by bees at 96°F. creates a 

 much lower relative humidity (18 per 

 cent) than the same quantity of water 

 at eoop. (58 per cent) because the 

 warmer atmosphere is capable of hold- 

 ing more water vapor, and relative hu- 

 midity is simply an expression of the 

 percentage present compared with all 

 that the atmosphere can hold. How- 

 ever, to maintain a temperature of 

 96°F. necessitates the consumption of 

 much more honey and this in turn 

 gives off much more water vapor. 

 Consqeuently with a cellar temperature 

 of 45°P. we should expect much more 

 condensation in a colony with a cluster 

 temperature of 96 °F. than in one with 

 a cluster temperature of only 65 °F., 

 except that the increased heat would 

 tend to produce stronger currents of 

 air in the hive which might relieve the 



situation somewhat. Since 96°F. is 

 about brood rearing temperature it is 

 partly indicated why brood rearing 

 during the winter confinement may be 

 highly injurious, as it is usually held 

 to be. It may be stated that a cellar 

 temperature of 45 op. and a cluster 

 temperature of 60°P. might not occur; 

 the other temperatures used in the 

 table might well occur under different 

 conditions. 



In making determinations of relative 

 humidity it is necessary to take into 

 account the barometric pressure but in 

 any given locality the changes of the 

 barometer are so small as to be neg- 

 ligible and therefore need not be dis- 

 cussed here. In any event in using 

 wet and dry bulb thermometers the 

 conversion table used must be for the 

 right barometric pressure. 



A further word of warning concern- 

 ing the use of wet and dry bulb ther- 

 mometers may not be amiss. To ob- 

 tain accurate results the air must be 

 moving past the bulbs at the minimum 

 rate of 15 feet per second and if this 

 is not occurring naturally the ther- 

 mometers must be whirled at a corre- 

 sponding rate. Unless this is done the 

 readings are entirely worthless. Great 

 care must be taken not to read the wet 

 bulb thermometer until it registers as 

 low as it will fall. It is therefore 

 obvious that wet and dry bulb ther- 

 mometers hung in the bee cellar and 

 not whirled give no reliable data as to 

 the relative humidity of the cellar. 

 Many bee-keepers thus use them, in- 

 correctly. 



How Moisture Escapes from the 

 Hive in Winter. During the summer 

 when nectar is being ripened into 

 honey, great quantities of water leave 

 the hive in the form of water vapor. 

 During this period the hive is being 

 well ventilated by fanning bees so that 

 the atmosphere is changed rapidly and, 

 being warm, is capable of taking up 

 more moisture than is the atmosphere 

 of the bee cellar. In winter when the. 

 bees are in a cluster this ventilation 

 by fanning does not occur. The 

 amount of water that must leave the 

 hive is much less than in summer but 

 on the other hand it either must pass 

 out in air set in motion by changes in 

 temperature or will condense on the 

 frames, combs and hive and possibly 

 run out by gravity. 



If the atmosphere of the bee cellar 



