l v i INTRODUCTION. 



ings and engravings, and Mr. F. D. Stuart, draughtsman of the Expe- 

 dition, for their aid in projecting the diagrams, and their assistance in 

 making the calculations for reduction to a common standard tempera- 

 ture and height, &c. 



The following are the corrections that have been applied to the 

 various instruments used on board the vessels to reduce them to the 

 Vincennes' standard. 



Vincennes' Marine Barometer, No. 1, +-090 till June, 1839; capacity 27 inches. 



" " " 2, + -001 remainder of cruise, " 



Peacock's " " " 1, 180 to 20th June, 1839, " 



" " 2, + -089 until broken, 1840, " 



" " " . " 3, +-122 from March, 1840, 



till July, 1841. " 



Reliefs " " + '074 whole cruise, " 



Porpoise's " " 4- "390 1839, " 



" Sympiesometer, +'570 to 15th January, afterwards +'230, 1841. 



The correction for capillary attraction has not been applied to any 

 of the observations that have been reduced ; the reasons for which I 

 would here assign, if my space would permit. I have, however, given 

 the capacity, and state that I believe the mercury to have been boiled 

 when filled. 



In conclusion, I desire to call attention to the general results of the 

 Meteorological Observations of the Expedition. Hitherto, I have 

 abstained, as far as possible, from giving anything but the facts, and 

 those I have stated have been for the purpose of illustrating the dia- 

 grams. The most remarkable phenomenon which our observations 

 have shown, is the irregular outline of the atmosphere surrounding 

 the earth, as indicated by the pressure on the mercurial column at 

 different parts of its surface. Our barometric observations show a 

 depression within the tropics, a bulging in the temperate zone, again 

 undergoing a depression on advancing towards the Arctic and Antarc- 

 tic circles. The difference between the northern and southern hemi- 

 sphere is equal to -929 in., whilst that between the eastern and 

 western sections (supposing the globe to be divided through the Ame- 

 rican Continent), will be '097 in. at the equator. On the east side, 

 at the parallels of 40 north and south, the pressure in the northern 

 hemisphere exceeds that of the southern by '231 in. On the west 

 side, on the same parallels, the difference is -171 in favour of the 

 northern. The difference of pressure on the western, exceeds the 



