56 PHILOSOPHICAL TRANSACTIONS. [aNNO 1666, 



be expected from some increase of heat : Such as have exact wheel-barometers 

 may try whether odours or fumes make the air Hghter. 



1 1 . He did not find in all this time the greatest changes of the quicksilver 

 to amount to more than 2^ or 2^- inches at most. 



12. He very often found great changes in the air without any perceptible 

 change in the barometer; as in dewy nights, when the moisture descends plen- 

 tifully. On the preceding and following days the vapours have been raised so 

 invisibly, that the air seemed very clear. Which rising and falling of vapours 

 import gravity and levity of air, and yet the barometer was not affected 

 by it. 



13. The barometer is sometimes not moved by very great changes in the 

 air; as December 18th, an extraordinary bright and clear day, and the next 

 following quite dark, some snow and rain falling, but the mercury kept at the 

 same height. So in high winds and calms, the same. 



14. December l6, l665, was a clear cold day, with a very sharp and strong 

 east wind ; the mercury very near 30 inches high ; about three in the after- 

 noon he saw a large black cloud approaching from the east and south-east, 

 with the wind at east. The mercury changed not that day nor the following; 

 the stars and most of the sky were very bright and clear till nine o'clock ; and 

 then the sky was suddenly overcast, yet no change of weather happened. De- 

 cember 17 th, the frost held, and it was a clear day till about two o'clock in 

 the afternoon ; and then many thick clouds appeared low in the west ; yet no 

 change of weather ; the wind, fnist, and quicksilver the sanrie. December 

 18th, the mercury fell almost i of an inch, and yet the sky and air were clear, 

 bright, and cold, with an east wind ; but accidentally sending his servant 

 abroad, he discovered the remote hills, about 20 miles off, covered with 

 snow. 



1 5 . He seldom observed the change to be very great at any one time ; so 

 that he once wondered to see that in one day it subsided about |- of an inch. 



16. January 13, 1 665-6, the mercury stood a quarter above 30 inches, as it 

 did also the day before ; yet both very dark and cloudy, and sometimes very 

 thick and misty air ; which is an uncommon case, for generally it stands higher 

 in the clearest settled weather than in such cloudy and misty fogs. This 

 thick air and darkness lasted above a week; lately more cold, and east and north- 

 east wind. 



17. In January \665-6, for many days it continued very dark, so that great 

 rains were apprehended, and though sometimes thick mists arose and some 

 small rain fell, yet the mercury stood at a great height ; which indicated no great 

 change of weather, and he was not disappointed. 



