VOL. LXX.] PHILOSOPHICAL TRANSACTIONS. 707 



Jan 14, the air became much warmer, and the barometer had now fallen -^. 

 Next day a thaw came on, and continued for some time. 



As the above experiment with the bellows favoured so little the opinion, that the 

 difference of temperature was caused by evapo- ^ Therm on Therm, in 



ration, Mr. W. wished for another opportunity °''"' the snow, the air. 



of making further experiments, and of in- | + 5 + 14 



quiring into circumstances still more atten- H + 4 + 11 



lively. A good occasion offered on Saturday, 2I . . ...... + 3.. .... + 11 



Jan. '22. The frost, which before this time had 2| + 3 + 11 



again returned, became on this night very keen ; i^ '.'.'.'.'..'.'+ i...... + 6 



and a good deal of the former snow yet remain- H + 6' 



o •' 5 — J + 5 



ing on the ground, the following observations ^^ ........— i..... . + 6 



and experiments were made at the observatory, 6^ — 1 + 6 



viz. on Sunday morning Jan. 23, at the several - , ,[,[,[., ^3'.'..,.. + 5 



hours the 2 thermometers pointed as in the 7| — 2 + /. 



annexed table. * 



Exper. 4. This night instead of blowing on the snow, Mr. W. fanned it by 

 means of a sheet of brown paper fitted to the end of a long slender stick. This 

 apparatus was previously cooled by lying on the snow, and in fanning he took 

 care to stand to leeward of the thermometer. The effect was, that the mercury 

 rose nearly to the same degree given by the thermometer in air at the same time. 



Exper. 5. At f past 1 o'clock, when the thermometer on the snow pointed 

 to -\- 3°, it was screened by 2 sheets of brown paper set up on their edges, and 

 so inclined againt each other as to stand. The paper had been previously cooled 

 by lying on the snow. At 2^^ the thermometer thus sheltered pointed to + 9". 

 This experiment was afterwards repeated with the same event. 



Exper. 0. Mr. W. next went up to the leads of the east wing of the observa- 

 tory. Here he hung a thermometer to the hook of a long pole, and raised it 

 in tne air about 24 feet from the ground, and at the same time inclined the pole 

 over the ballustrade, so as to put the instrument fully to windward of the house. 

 On suddenly lowering the pole, after half an hour, and examining the ther- 

 mometer, the air at that elevation was found to be pretty constantly 4" warmer 

 than at the station below. 



Exper. 7. The result of this trial appeared more remarkable than any thing 

 which had hitherto occurred. Mr. W. lowered the pole till the thermometer 

 was brought down within half a foot of the ballustrade, but keeping it still a (ew 

 inches to windward of the building; and by this means it was found that the air 

 here was never colder than -|- 10°. On the ballustrade there happened to be 

 several detached bodies which had attracted a very thick hoar-frost. When the 

 thermometer was taken off the hook of the pole, and laid on this hoar-frost, 



4x2 



