172 



Mr Glazebrook, On the effect of moisture in [Oct. 27, 



after it has been continued for some time the reading rises to 

 above its normal value falling back to it in time. 



This is shewn in the observations for July 28, the glass 

 having not been rubbed since July 22. These are given in the 

 Table column (1) shewing the conditions under which the readings 

 were taken, and (2) the actual reading. The normal condition 

 means without blowing either dry or damp air on the surface. 

 The angle of incidence was about 45°. 



After an interval of an hour the normal reading was 32° 44'. 



The temperature changed during the observations from 19° to 

 20°. 



Thus in this case damp air produces, while being blown, an 

 effect of the same sign as the dry but of greater magnitude, while 

 the effect observed just after the blowing has ceased is opposite 

 to that due to dry air. 



If however the surface has been rubbed with a dry leather 

 immediately before the damp air is blown the reading is raised at 

 once without the previous lowering. 



A very full set of observations taken on August 6 shew the 

 two effects. 



Time. 



Conditions. 



h. m. 



1 7 

 1 15 



1 21 

 3 18 



4 P.M. 



4 25 



5 23 



5 30 

 5 35 



Normal ... 



Dry air blown 



Normal 



Damp air, at first 



then 



and finally 



Normal 



Normal 



Damp air, at first 



then 



and immediately after stopping 

 Glass rubbed. 



Normal 



Damp air blown 



immediately after stopping . 



and 



Glass rubbed. 



Normal 



Damp air blown 



Normal 



Dry air blown , 



Normal 



Beading. 



35° 8' 



35° 4' 30" 



35° 8' 15" 



34° 59' 



35° 7' 



9' 30" 

 8' 30" 

 9' 30" 

 3' 

 9' 



35° 

 35° 

 35° 

 35° 

 35° 



35° 13' 



35° 8' 30' 

 35° 15' 

 35° 15' 

 35° 12' 



35° 8' 

 35° 10' 30" 

 35° 7' 30" 

 35° 5' 

 35° 9' 



