1865.] On the Circulation fyc. of the Atmosphere of the Atlantic. 345 



IX. "On the Normal Circulation and Weight of the Atmosphere 

 in the North and South Atlantic Oceans, so far as it can be 

 proved by a steady Meteorological Registration during five 

 Voyages to India." By Captain HENRY TOYNBEE. Commu- 

 nicated by Major-General SABINE, President. Received June 8, 

 1865.. 



Having lately made five voyages to India, leaving England on the 1st of 

 July and returning early in April, I have observed the recurrence of certain 

 facts relating to the weight and circulation of the air in the same part of 

 the world at the same seasons of the year, from personal registration of 

 the barometer, wet- and dry-bulb thermometers, direction and force of the 

 wind, &c., five times daily. 



These five voyages have carried us through the Atlantic Oceans from 

 50 N. to 40 S. lat. in the months of July and August ; again returning 

 home, we have passed from 34 S. lat. to 50 N. lat. during the months 

 of February and March each year. 



The accompanying diagrams * show the height of the barometer at noon 

 in each degree of latitude; and as we were not in each degree exactly at noon, 

 interpolation has been used : for instance, if in 24 N. lat. at noon the 

 barometer were 30' 12 inches, and in 22 N. lat. it were 30' 10 inches, it has 

 been called 30-11 inches in 23 N. lat. This plan is not to be trusted, how- 

 ever, on the polar side of the trade-winds, where the barometer is constantly 

 undergoing change, depending upon a series of independent gales, of which 

 something will be said by and by ; but it seems to give very correct results 

 in and between the trade-winds, where the height of the barometer had 

 long been noticed to depend chiefly upon the latitude and season of the year 



We will first allude to the five diagrams representing the outward pas- 

 sage, the two upper ones lying to the west, or outside the Cape Verde 

 Islands, the three lower ones to the eastward, or between them and Africa. 



The first facts they prove are, that the barometer at this season ranges 

 lower to the eastward than to the westward of the Cape Verdes, the N.E. 

 trades extending further south to the westward, and the S.W. monsoon 

 (which at this season blows between the trades) sets in further north, and 

 blows stronger the nearer to Africa. 



We are told that the Great Sahara Desert being heated by the sun of 

 the northern summer causes an upward current of air, which draws in the 

 air from the sea to restore equilibrium, just as the heated lands in India 

 during the same season cause a S.W. monsoon in the Bay of Bengal, where 

 a N.E. trade would otherwise prevail. Our barometer diagrams show this 

 by being lower near Africa, and gradually rising as the distance from the 

 demand is increased. Again, in about 13 N. lat., where the S.W. mon- 

 soon commences, it is always much more from the west than it is further 

 southward, where the wind draws to the south, and very generally turns 



* The Barometric Curves and Track-Chart are preserved for reference in the Archives. 



