MR. W. N. SHAW OX HYGROMETRIC METHODS. 



10U 



but the deposit was not then very large, though quite 

 distinct. 



On September 4, the day after Experiment 81, observations were made with DINER'S 

 instrument, but no observation with the chemical method was made. 



The object of the experiment was to watch for the deposits of the dew when the 

 temperature of DINES was maintained as nearly as possible at constant temperatures. 



The following are the observations : 



Experiment 83. 



Time. 



b. in. 



;{ -28 



3 30 



3 45 



3 52 



3 55 



4 

 4 6 

 4 20 



4 35 



4 46 



5 7 



hfanfar. 



15-09 

 15-01 



15-00 

 14-98 

 15-00 

 15-00 

 15-00 

 15-01 



15-02 



Air 

 temperature. 



16-Ot 



Thermometer ran slowly down : dew 6rst showed at the near end at 



l.Y'-U'i. and gradually extended all over the further side while the 



thermometer fell ultimately to 12'2; the deposit continued to 



increase, but only on the same portion of the surface. 



Dry air passed through and deposit removed. 

 Dry air stopped and damp air sent through. DINES reading 12'89. 



Deposit formed on a portion only of the face. 



Deposit removed by dry air. 



DINKS, 13'89 ; damp air turned on and gave a deposit after some time. 

 DINKS, 14'44; damp air put on; dew visible iu 1m. 45s. Dry air put 



on ; dew gone in 11s. 

 DINES, 15'00. First sign of dew visible at 1m. lls. after starting air. 



DINKS wab then standing at 15'22; it rose to 15 44, the dew still 



remaining. 

 DINKS, 15 '56; damp air sent through, a very faint deposit of dew 



appeared, which did not disappear until the thermometer had reached 



15*72. 

 DINIS cooled again slowly. First indication of dew at 157, very 



faint; water stopped, and thermometer fell to 15'4, and dew slightly 



increased. Still on at 15 r '6, rather fainter at 16*'l. 

 The deposit did not completely disappear until the thermometer 



reached 16-94. 

 The water was then run through still more slowly. A deposit of dew 



was visible when the thermometer reading was 16"2, and the water 



was then kept just flowing. The thermometer reading never went 



below 16'l, but the dew deposit was quite distinct. 

 Damp air turned on, and last observation repeated. Started at 167 ; 



dew began to form almost immediately, and the flow was stopped, 



the thermometer fell to 15'8, showing increase of dew without 



further supply. 



To verify that there was a rail deposit, and not an incidental 



reflexion, the tap was turned and dry air sent through, the spot on 



the glass being carefully watched. The cloud distinctly cleared off. 



24. It will be seen from these experiments (Nog. 78 and 79) that the temperature 

 of the water in the interior of the metal box, of which the glass surface forms the lid, 

 is not necessarily uniform. If the flow is very slow a narrow current is established 

 through the box and a deposit forms along it, the other part being left bare (Experi- 

 ment 81). The facility of reading is much improved by a circulation of the air 



