338 



THE BEE-KEEPERS' REVIEW 



power and the surplus, which can- 

 not be held, is deposited on the 

 surface of the glass. These drops do 

 not "sweat" through the glass, as 

 the common expression would indi- 

 cate, but are condensed from the 

 surrounding atmosphere. Similarly 

 we may have condensation when the 

 surface of the earth is cooled and 

 this we call "dew" if it remains 

 liquid and "frost" if it is frozen 

 as it condenses. Other examples 

 come to mind at once for such 

 phenomena are common. Dew ap- 

 pears not to form so readily if a 

 strong wind is blowing for it eva- 

 porates as soon as formed. It is of 

 course obvious that when the tem- 

 perature of the air again rises the 

 moisture deposited as dew may be 

 taken up by evaporation. These 

 homely examples find their exact 

 parallels in the bee hive and bee 

 cellar. 



To eliminate moisture which 

 leaves the body of the bee in the 

 form of water vapor without con- 

 densation is, in brief, the problem 

 which the beekeeper is trying to 

 s^lve. This may be accomplished in 

 actual practice by raising the tem- 

 perature of the outer air, drying 

 the air (as by the use of unslaked 

 lime) or by causing it to move so 

 that as the atmosphere becomes 

 fully laden with water it will be 

 replaced with other air capable of 

 taking up still more moisture. Var- 

 ious beekeepers accomplish this by 

 any one of the three methods, all 

 of which are fairly successful. 



Absolute humidity, or the meas- 

 ure of the amount of water ^^apor 

 in a given space, is expressed in 

 the actual weight of the water in 

 this space. This is difficult to ob- 

 tain directly in ordinary practice 

 and the usual method is to deter- 

 mine relative humidity, that is 

 the amount of moisture in the at- 

 mosnherp compared with the maxi- 

 mum which might be held at that 

 temperature. The comm'^n method 

 for determinins; this is bv the use 

 of wpt and dry bulb thermometers, 

 to determine how much the wet 



* Consult Marvin, C. F. 1912 Psychro- 

 mptric tnblps for ohtninincr vapor pre.s- 

 sure, relative humirlity and tomperq- 

 tnre hiimirlitv anrl tempprature of the 

 dew-noint. U. S. Pept. of Ap-rie. "Weath- 

 er Bureau CNo. 2^,^) and Si-nithsonion 

 meteorolofiioal tables, fird Fd. Smith- 

 sonian Institution INTo. 1032 Miscell. 

 col. Pt. of Vol. XXXV, 



bulb is cooled by evaporation. From 

 these data we then determine the 

 relative humidity from prepared 

 tables (see above reference). 



To make clear the relation of 

 the relative humidity to tempera- 

 ture it may be well to choose a 

 few examples. For the first case, 

 let us assume a cluster temperature 

 of 60" F. in an atmosphere which 

 is fully saturated. In this event 

 the slightest cooling will cause con- 

 densation and the wet bulb in such 

 an atmosphere (if it could be circu- 

 lated rapidly) would show no cool- 

 ing. No evaporation can occur as 

 the atmosphere cannot take up any 

 more moisture. If however the wet 

 bulb can be cooled at this temper- 

 ature the relative humidity is less 

 as the readings of the wet bulb 

 thermometer are lowered. The 

 temperature to which an atmosphere 

 must be cooled to produce condens- 

 ation is known as the "dew-point." 

 This is also lowered as the humid- 

 ity decreases. These points are il- 

 lustrated in the accompanying 

 table. 



As.snmed cluster 

 temperatures 



Drv 

 buib 



Wet 

 bulb 



Dew 

 point 



Relative 

 humidity 



60° 

 60° 

 60° 

 60° 

 60° 

 60° 

 60° 



P. 

 P. 

 P. 

 P. 

 P. 

 P. 



60° P. 



58° 

 56° 

 54° 

 52° 

 50° 



P. I 48° 



P. 

 P. 

 P. 

 P. 

 P. 

 P. 



60° 



57° 



5n° 



49° 

 45° 

 40° 

 35° 



P. 

 P. 

 P. 

 P. 

 P. 

 P. 

 P. 



100 



89 



78 

 68 

 58 

 4S 

 39 



percent 

 percent 

 percent 

 percent 

 percent 

 percent 

 percent 



With such an assumed tempera- 

 ture of the cluster (60° F.) only 

 the highest relative humidities 

 would show condensation in a cel- 

 lar in which such a cluster temper- 

 ature would be found. 



Let us examine this from anoth- 

 er angle. If we assume different 

 temperatures for the cluster (all of 

 which have been observed under 

 different conditions by various in- 

 vestigators) let us see what the 

 relative humidity of the warmer 

 atmosphere must be not to show 

 condensation when cooled to cellar 

 temperature. The following table 

 gives these data: 



Assumed cluster 

 temperatures 



~"Dry \ Wet 

 J3ulb_ \_ bu lb 



60"° P. I 52 

 65° P. I 54 



Relative 

 humidity 



P. I 45° P. 



P. I 45° P. 



75° P. 1 58.5° P. I 46° P. 



96° P. I 66 ° P. I 45° P. 



58 percent 



48 percent 



35 percent 



18 percent 



