80 REPORT—1845. 
Prague and Greenwich ; viz. a correspondence of the maximum of vapour 
pressure and minimum of gaseous pressure with the maximum of tempera- 
ture,—and of the minimum of vapour pressure and maximum of gaseous 
pressure with the minimum of temperature; and a progressive march of the 
three variations from the minimum to the maximum, and back to the mini- 
mum again. The epochs, or turning-points of the respective phzenomena, are 
not in every case strictly identical ; but their connexion, which is the subject 
immediately before us, is most obvious. 
We have thus a further illustration of the universality of the principle of 
the dependence of the regular periodical variations, annual as well as diurnal, 
of the pressures of the dry air and of the vapour, on those of the temperature *. 
* In the tropics and in the temperate zone the heat of summer produces and accompanies 
a low gaseous pressure, and the cold of winter a high gaseous pressure. When we consider 
how large a portion of the northern hemisphere is occupied by land, which becoming greatly 
heated in summer rarefies the superincumbent atmosphere, causing it to overtop the adjacent 
less heated masses, and to overflow them, we should be led to expect that in parts of the 
Arctic Circle situated to the north of the great continents, the gaseous pressure should be 
increased in summer, and that the curve of annual variation should become the converse of 
what it is in the lower latitudes. It appears from the meteorological observations made in 
1843 by Messrs. Grewe and Cole, and presented to the British Association at the York meet- 
ing by Dr. Lee, that such is the case at Alten, near the north cape of Europe. The barometer 
and thermometer were observed three times a day, from October 1842 to December 1843 
inclusive. The hours of observation were 9 a.m., 3 p.m. and 9 p.m. No hygrometric 
observations were made, but we are able to infer the approximate tension of the vapour from 
the record of the thermometer. The quarterly means of the barometer and thermometer in 
1843 are as follows; the barometer being reduced to the level of the sea, and corrected for 
gravity :— 
Barometer. Thermometer, 
in. 
December, January, February...... 29°375 24 F. 
March, April, May .........00 wcoeee 29°948 27-7 
June, July, August .....s..eeseeee -- 29:905 52°4 
September, October, November... 29°716 34:2 
Mean of the year ......... pesscancdeeel (ea 4a0 34:6 
Assuming the humidity in each quarter of the year to be 75, or the vapour to be in each 
case three-fourths of that required for saturation at the respective temperatures, we should 
have the following gaseous pressures :— 
in. 
December, January, February ........sseeseeeenee. 29°257 
March, April, May ...cccccccsesesceesece Sigaivcres> 29-804 
June, July, August .......csccceeeseeees sessesecneee 29'616 
September, October, November, December ... 29°566 
29-561 
It appears therefore that in the six summer months the mean barometric pressure exceeded 
that of the winter months by 0°381 inch; and the mean gaseous pressure of summer ex- 
ceeded that of winter by about 0°3 inch. As in this case the curve of the gaseous pres- 
sure, as well as that of the aqueous vapour, accords in character with the curve of tempera- 
ture, i.e. ascends with ascending temperature, and descends with descending temperature,— 
the barometric annual range is greater than the gaseous annual range, which is contrary to 
what takes place in the temperate and equatorial zones. It is not improbable that in the 
Antarctic Circle the phenomenon which we have just noticed as taking place in the Arctic 
Circle, viz. the summer increase of the gaseous pressure,—may not be found in the same degree, 
if at all; for the two hemispheres present a remarkable contrast in their respective propor- 
tions of sea and land, and the rarefaction of the atmosphere over the middle latitudes of the 
southern hemisphere during its summer must be greatly less than in the same latitudes of the 
northern hemisphere in the corresponding season. The barometrical observations made by 
Sir James Ross in summer in the Antarctic Circle accord with this inference ; since after cor- 
recting them for the shortening of the column of mercury by the increased force of gravity 
in the high latitudes, and abstracting the small tension of vapour corresponding to the tem- 
perature, the mean gaseous pressure deduced from them, though nearly equal to the mean 
gaseous pressure of the year at Bombay, does not exceed it; whereas at Alten it is only im 
a — 
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