REPORT ON ATMOSPHERIC CIRCULATION. 55 



skies clear. Hence, latitude for latitude, temperature is highest in India and in the 

 inland United States to the westward of the Mississippi. The most uniformly distri- 

 buted temperatures are over the Indian Ocean to the north of lat. 20° S., and in the 

 Pacific between lat. 20° N. and S. On the other hand, the isothermals are much 

 crowded over North America generally, in Senegambia, and South Africa. 



As compared with March, pressure has risen over nearly the whole of the southern 

 hemisphere ; and in the northern hemisphere, to the north of a line drawn from the 

 mouth of the Mackenzie River to Anticosti, then south-west to near Cape Hatteras, 

 then through the Atlantic eastward to long. 33° W., then northward to lat. 55° N., 

 then eastward to the Ural Mountains, and thence to Cape Severe Over this latter 

 region the largest increase, being from 0'15 to 0"20 inch, is from West Greenland to 

 the mouth of the Obi. Pressure has now fallen from two to three-tenths in the centre 

 of Asia, whereas in the centre of North America and of Europe the fall only slightly 

 exceeds one-tenth. Over the Arabian Sea and the Bay of Bengal, while pressure has 

 fallen 0"04 to - 08 inch, it has fallen over India between these two seas from - 08 to 0"15 

 inch, or nearly double ; and in India the greatest decrease is in the north-west, where 

 the air is driest and temperature is rising most rapidly. The conserving influence of 

 the Mediterranean on the pressure is equally striking. Again, in the North Atlantic, the 

 cold Labrador current, with its low temperature and increased pressure, and the warm 

 southerly current on the east side, with its greatly diminished pressure, suggest 

 interesting connections between changes of pressure and relative surface temperatures. 



The high pressure of Central Asia has now all but disappeared, and the high 

 pressure area of the Arctic regions, extending from Lake Superior to Northern Siberia, 

 reaches the annual maximum, the absolute maximum isobar extending from the Arctic 

 Circle in long. 105° W. in a W.N.W. direction to the Liakov Islands. The other 

 anticyclonic regions are Southern Australia, in the Indian Ocean to the south of 

 Madagascar, and the four regions in the Atlantic and Pacific immediately to the west 

 of the old and new continents. It is remarkable that the highest of these, where the 

 mean pressure rises to 30-30 inches, is the one to the west of California, the next 

 highest being the anticyclone in the Indian Ocean, where pressure only reaches 

 30 '15 inches. 



Except the Antarctic depression, none of the low pressure areas are strongly 

 marked. The cyclonic regions of the North Pacific and Atlantic are now much reduced 

 in depth and extent ; while, on the other hand, that of India has deepened and extended, 

 and new centres of depression have begun to appear in the region of the Rocky 

 Mountains, and in the Pacific to the west of Panama. 



May. — As regards temperature, the most noteworthy feature in this the transition 

 month from spring to summer of the northern hemisphere, is the high temperature 

 which prevails in all tropical and sub-tropical regions, particularly where the rainy 



