470 Mr. W. Brown on the Differences of 



of any doubt as to its general correctness. Without inserting 

 here its details, it may be of use to give its principal features 

 in a tabular form. 



Name of place. North lat. Height of barom. Increase. 



Christianborg 5° 24' 29-8t9 



La Guayra 10° 48' 29-8.56 -007 



Macao 22° 10' 29-985 "129 



Madeira* 32° 37' 30'093 -108 



43° 47'^ Decrease. 



Mean of four places ... to > 30-001 -092 



45° 24' 



53° S2'° 

 Mean of five places to J- 29-942 -059 



55° 51' 



64° 00' 

 Mean of three places... to )■ 29-675 -267 



65° 50*^ 



73° OO'l Increase. 



Mean of three places ... to V 29-843 -168 



75° 30' J 

 From this it appears that the mean pressure of the atmo- 

 sphere is greatest at latitude 32° ; decreasing on each side of 

 it, but in the greatest degree towards the pole, its minimum 

 being at latitude 64° ; whence it again increases until 75°, 

 that being the limit of the observations, though from the regu- 

 larity of the variations, we may infer that the increase goes on 

 to the pole itself. 



Now it is obvious that these results are quite contrary to 

 what would be produced by a constant, or almost constant 

 opposition to the influx of air towards tropical latitudes ; as 

 this would occasion an accumulation of air in high latitudes, 

 and a corresponding deficiency in regions near the equator. 

 But were there no counteracting cause, the same effect would 

 result from other circumstances. It would be the natural 

 consequence of two currents flowing in opposite directions be- 

 tween the pole and the equator. As the air flowing towards 

 the pole surrounds during its course, circles of constantly 

 diminishing diameter, it will occupy a smaller horizontal area, 

 and will arrive in high latitudes in over abundance; whilst 

 the lower current for the same reason will bring an insuffi- 

 cient supply to the atmosphere encompassing circles of greater 

 diameter ; an effect which would be yet further increased by 

 the retardation of the lower current by friction on the surface 



* By referring to the table from which these numbers are taken, it will 

 be seen that the height for Tripoli (latitude 3255) 30-182 inches is 

 omitted ; this however is obviously an error. 



