The Low Barometer of the Antarctic Temperate Zone. 337 



so much more complicated in the northern than in the 

 southern hemisphere. Neglecting these (as in Fig. 2, which 

 represents for the northern hemisphere the relations corre- 

 sponding to those exhibited for the southern hemisphere in 

 Fig. 1), we see that there is a much greater resemblance 

 between the rise and fall of barometric pressure as we proceed 

 northwards than as we proceed southwards. In fact, the curve 

 is almost exactly symmetrical on either side of 30° north lati- 

 tude to the equator on one side, and to latitude 60° on the 

 other. From 60° the pressure continues to diminish for awhile, 

 but appears to attain a minimum in about latitude 73°, and 

 thence to increase. In the southern hemisphere, if there is 

 any corresponding minimum, it must lie in a latitude nearer the 

 south pole than any yet attained. 



The most marked feature in the comparison of the two 

 hemispheres is the difference of pressure over the southern 

 and northern zones, between latitudes 45° and 75°. This is a 

 peculiarity so remarkable, that for a long time many meteoro- 

 logists considered that the observations of Captain Ross were 

 insufficient to warrant our concluding that so important a 

 difference really exists between the two hemispheres. But 

 not only has Captain Maury — from a comparison of 7000 ob- 

 servations — conhrmed the results obtained by Ross, but, in 

 meteorological tables published by the Board of Trade, the 

 same conclusions are drawn from 115,000 observations, taken 

 during a period of no less than 13,000 days. In fact, it is 

 now shown that the difference is yet greater than it had been 

 supposed to be from the observations of Captain Ross. From 

 a comparison of observations made in the Antarctic Seas with 

 those of Captain Sir Leopold McClintock, it appears that the 

 average difference of barometric height in the northern and 

 southern zones, between latitudes 40° and 60°, is about one 

 inch. Figs. 1 and 2 exhibit a relation midway between these 

 later results and those tabulated above. 



Assuming an average difference of only three-quarters of 

 an inch in the northern and southern zones, between latitudes 

 40° and 60°, let us consider what is the difference of pressure 

 on these two zones of the earth's c urface. The area of either 

 zone is 21,974,260*5 square miles, and the pressure on a square 

 mile due to a barometric height of three-quarters of an inch 

 is about 670,000 tons, therefore the pressure on the northern 

 zone, between the latitudes named, exceeds the pressure on 

 the southern zone by no less than 14,500,000,000,000 of tons. 

 Including all latitudes within which there has been ascertained 

 to be a difference of barometric pressure in the two hemi- 

 spheres, we shall probably be within the mark if we say, that 

 the atmospherical pressure on the northern hemisphere is 

 vol. xi. — no. v. z 



