¥: we a] 3 — i oe 
Pe e - ‘ 
fe 364 On Storms and Meteorological Observations. 
j results. It is not meant to te asserted that mean results are of no 
we t we must not hope to deduce many of the great laws of na- 
> ture from them.. ‘This were much as if a chemist should. set down 
in a table all the ; alkali, alcohol, etc. consumed in his laboratory 
in the course te year, with all the resulting substances of what- 
ever kind, and rtake to derive thee these data the erent fanda- 
— doctrines of his science. : wl 
» No record of the height of the mercury in the barometer can he 
of value unless the instrument is both carefully purget of air and | 
filled with mercury whose specific gravity has been correctly ascer- 
dained. It is'somewhat remarkable, when we consider the many la- 
borious observations that have been. made in. various. parts of the 
world, the plans that have been proposed for clearing the tube com- — 
ely of air, and the contrivances added for reading off the altitude 
to the thousandth part of an inch; that the constant and perhaps ne- 
‘cessary uncertainty of the standard itself should have been so much 
es neglected. ‘The mercury employed by Mr. Daniell in filling the 
of the barometer recently made for the Royal Society, was 
7 by Mr. Faraday’to have a specific gravity of 13. 624 at 40° — | 
| of Fahrenheit’s thermometer, the temper ature of the water being the | 
“«  game—or of 13.609 at the temperature of 60°. He states the 
mean height of the barometer in London at'29.881 inches. But 
ae Dr. Bency in the last edition of his Cher ry makes the specific | 
~~ gravity of mercury 13.545 at 47° of Fahrenheit, or 13.538 at 60°. - 
f Daniell’s mean altitude was obtained with the same’ metal, or with 
metal of the same specific gravity with that employed in filling the 
‘syal Society’s barometer ; the mean height with Dr. Henry’s mer- 
‘would be 30.038. But Dr. “Thomson, remarking that the spe- 
S gravity of mercury “ varies considerably like that of all other 
’ says that he once obtained it as low as 13.4228. ‘This would | 
ac -ording to Daniell at 30.295. We have therefore the fol- 
ng numbers: 
* Height of the hatowictes 4 in London as deduced by Luke Howard 
~ from the register kept at the rooms of the eile Society, 2 mean 
of twenty years, 29.8655 
Height stated by Daiell—supposed sect _— 
‘ of, the mercury, 13.609, pre 
— sure . 
i Height ith Dr. Henry’s mercury—same pe , cas 
- Uncertainty depending upon the variable” ipeeieeie sas 
2 4295 
_ gravity of the = : a 
,° ith Dr. Thompson’s mercury, - pte 
