REPORT ON ATMOSPHERIC CIRCULATION. 57 



The low-pressure system of India has shifted a good way to north-westwards, 

 and deepened to 29 '60 inches, and those of Central Africa to 2970 inches, of North 

 America to 29 - 80 inches, and of the Pacific, near Panama, to 29 "85 inches. On the 

 other hand, the cyclonic systems of the North Pacific have shallowed to 2975 inches, 

 and that of the North Atlantic to 29 "90 inches, and in the adjoining parts of Europe 

 there are five other centres, each of very limited extent, where pressure has fallen 

 slightly lower than 29 "90 inches. 



June. — This is the first summer month of the northern hemisphere, and the isother- 

 mals have now taken their summer positions. The highest isothermal, 95°, appears 

 in three regions, viz. in India, in Central Africa, and in North America. The summer 

 isothermals are thrust further than anywhere else into higher latitudes in North America, 

 from Mexico in a N.N.W. direction as far as the head waters of the Yukon. Over the 

 whole of this region the climate is drier, and sunshine consequently stronger, than over 

 the regions to the east and west of it. The isothermals occupy also higher positions in 

 latitude over the Europeo-Asiatic continent, unless where the influence of sheets of 

 water draws them into lower latitudes ; and the remarkable parallelism of the lines in 

 the more strictly inland climates is one of their most marked features. The influence 

 of the ocean in maintaining a low temperature as compared with the land in the east of 

 Asia from the Sea of Okotsk to China, and in the east of North America from Labrador 

 to south of Cape Hatteras, is more pronounced than in any other of the warmer months 

 of the year. 



The almost equal lowering of the isothermals in the northern portion of the Pacific 

 on each side of Behring Straits is very remarkable, and is in striking contrast to the 

 totally different distribution of temperature which obtains in the same latitudes of the 

 North Atlantic. 



Mean temperatures under the freezing point are now wholly within the Arctic 

 Circle. 



The changes in the distribution of the pressure are a diminution over the whole of 

 Asia, amounting to about two-tenths near the centre of the continent ; all Europe, 

 except the northern part of Scandinavia and Italy, Switzerland, the southern half of 

 France, and the Peninsula ; all North America, except the extreme south-east and the 

 extreme north-west of the continent ; and in the southern hemisphere, in New Zealand 

 and the extreme south of Australia. Elsewhere pressure has risen, the greatest increase 

 being in the Atlantic from Spain westward to long. 30°, and in the south of Africa. 

 One of the most widespread changes in the distribution of pressure occurs from May to 

 June, which ushers in the summer months of the northern hemisphere. It embraces 

 nearly all the southern hemisphere, the Atlantic south of lat. 55° N., the increase 

 flowing over so as to cover parts of Europe and North America. 



The anticyclonic regions of high pressure are the four in the North and South 



(PHTS. CHEM. CHALL. EXP. — PABT V. 1889.) 6 b 



