SJT Mr Hopkins on the Influence of 



tion ; but the sincere and ardent searcher after truth, in ex- 

 ploring the dark regions of the past, must feel himself bound 

 to speak of whatever a ray from the intellectual torch may 

 reach, even though the features of the object should be but 

 dimly revealed. — Fly mouth British Association Report, p. 191. 



On the Influence of Mountains on Temperature in the Winter 

 in certain parts of the Northern Hemisphere. By Mr 

 Hopkins. 



It was stated by Mr HopkiiiS; at the Plymouth Meeting of the British 

 Association, that between the latitudes of 40° and 70,° north, there is, in 

 the same parallels, a great difference of temperature, particularly in the 

 winter, amounting, in some cases, to as much as 40° or even 50° of Fah- 

 renheit. The western coasts of the two continents are much warmer than 

 the eastern^ and the winds generally blow from the sea to the western 

 coasts ; and it has been inferred that the prevailing winds passing over 

 sea to the western coasts, and over laud to the eastern, was the cause of 

 the difference in the temperature. This inference is not, however, in ac- 

 cordance with facts, as the low temperature is not proportional to the 

 distance from the western coast. Throughout this part of the northern 

 hemisphere, it i-i found that climate has certain relations to the elevation 

 of land, not simply arising out of the elevation of that part of the earth's 

 surface above the general level, but out of the influence which the eleva- 

 tion exercises on the atmosphere. (Here a diagram was exhibited, illus- 

 trating Hadley's theory of the atmospheric currents.) This theory re- 

 presents the tropical atmosphere as rising and flowing over at the top to- 

 wards the polar regions, and returning when cooled, flowing along on the 

 surface of the earth. This inequality of temperature in the atmosphere 

 would cause an upper current to flow north, and an under current to flow 

 south. But the unequal velocities of the different parts of the earth's 

 surface, from the equator to the pole, modify the course of these cur- 

 rents, and make the upper a south-west, and the lower a north- cast 

 current, as shewn by lines on a Mercator's chart. This theory, true 

 in its leading principles, does not account for what occurs on the earth's 

 surface, because it does not take in all the causes that are in operation ; 

 which causes materially modify the general results. The polar current, 

 in flowing from the north-eastern part towards the south-west, meets 

 Avith elevations of the land, and is, consequently, along a diagonal stripe 

 in the direction of the general currents, obstructed in its progress, and 

 sometimes stopped, and obliged to turn back, as an upper current, to- 

 wards the pole ; while beyond the obstruction, nearer to the equator, the 



