58 METEOROLOGICAL 



The bai'ometer, which is an upright one of 

 the usual construction, lias a tube 32 inches 

 long, with a capacious bulb at its lower extre- 

 mity ; its internal diameter is .22 of an inch, 

 and it was carefully filled with dry mercury. 

 No allowance having been made on the scale for 

 the rise and fall of the mercury in the bulb, the 

 variations, as registered, are somewhat too small : 

 to be strictly accurate, they should be increased 

 by one-fortieth part. 



The height of the instrument above the level 

 of the sea, I have reason to believe, is about 

 292 feet. From barometrical measurements, I 

 find its elevation above the Duke of Bridgewater's 

 canal, at Manchester, to be 212 feet, and the 

 canal is represented to be nearly 80 feet above 

 the sea,* making a total of 292 feet. 



Many observations were taken each day during 

 the foregoing period of eight years, but the highest 

 and lowest only, with the mean obtained from 

 them, were regularly noted down in the journal. 

 Previously to any observation being made, a few 

 gentle vibrations were invariably given to the 

 mercury for the purpose of overcoming its adhe- 

 sion to the tube. 



* Society's Memoirs, New Series, Vol. IIL p. 486. 



