//f Mini I y h'lu oAv >rRs 243 



As one of ilu- (lilVuiiltii's i-iuoiintcrril in llio use of ilu' wi'i hull) iIrt- 

 moim-ter consists in the graiiual rlonninR and drying up of the wick 

 due to the accumulation of impurities left in it from the evaporatiotv 

 of the water, together with the dust which settles from the air whic h is 

 drawn over it, special care must be taken to guard against troul)le 

 from this source. The cotton fabric used for the wicks which cover 



Fig. 4 — Ventilated Psychrometer 



the wet bulb must be treated to remove all traces of grease, with 

 subsequent thorough washing to remove all traces of corrosive material. 

 .After this, the wicks should Ix; handled only with thoroughly cleaned 

 hands before they are placed on the thermometers. These wicks 

 should be changed daily. Pure distilled water must be used in the 

 tanks and they must be cleansed occasionally because they become 

 contaminated by the impurities washed out of the air as it bubbles 



