from Dec. 1823, to J^c. 1824. ^%& 



'. From the annual mean pressure at these places, I infer that 

 Mr. Gary's barometer is placed 30 feet above the low-water 

 ^ark of the river Thames, and that Mr. Veall's is 200 feet 

 above the low-water mark of the river Witham, mine being 50 

 feet above the low- water mark of Portsmouth harbour. This 

 inference is made upon the supposition that the mercury iij 

 each of our barometers is of the same specific gravity, and 

 similarly affected in its contractions and expansions by equal 

 pressures of the atmospherical column. I suspect, however, 

 that 200 feet is a great deal higher than Mr. Veall's barome- 

 ter is placed above the low-water mark of the river Witham ; 

 and that 30 feet is lower than Mr. Gary's is placed above 

 the low-water mark of the Thames ; especially as the tide rises 

 19 feet in the latter river. 



I am and have long been of opinion that correct barometers 

 will never be procured by our meteorologists in different parts 

 of the country, till the cause is taken up by such scientific 

 men as those who form the Meteorological Society, and the 

 manufacturing of them confined to experienced artists under 

 their superintendence : for some use barometers made by 

 one artist, and others by other artists; and it is doubtful 

 whether all those who register their observations confine them- 

 selves to the portable upright barometers, which are the most 

 simple in construction, and far more correct and equal in the 

 scale of their movements by equal pressures, than the wheel- 

 barometers can be, from the friction to which they are liable, 

 and the ujicqual propoition of their jmllei/s to the circumference 

 of the scales. I have seen wheel-barometers of an elegant ap- 

 pearance at the time of a very low pressure, (as that on the 

 Sith of December 1821,) belov.' the range of their scales of 

 from 28 to 31 inches; the index of one was x'oths, of another 

 •Aths, and of a third nearly y'^jtlis of an inch below the bottom 

 ot the scales; while the mercury in the upright barometers in 

 the same neighbourhood and at the same height did not sink 

 below 28*10 inches — the lowest I ever observed it in mine. I 

 trust the members of the Meteorological Society will not deem 

 my suggestion obtrusive, as they are well aware of the great 

 discrepancies in the indications of barometers at difterent 

 places and at the same height from the level of the sea, and 

 of the jierplexity they occasion to observers in making their 

 comparisons even with mean annual pressures. The next 

 circumstance that claims my attention in the foregoing table 

 is the temperature of the external air. It appears that the 

 mean ol' Mr. Gary's thermonieter this year, at 8 o'clock A.M., 

 is about 3^ degrees lower than the mean of mine at half-past 

 8 A.M. From a knowledge of the annual mean tempei'atiu'e 



Ci g y oS 



