114 MR ROBERT C. MOSSMAN ON THE METEOROLOGY OF 



gradients for north-west winds south of 50° S. on the Pacific side, with comparatively 

 slight gradients and a subnormal gale-frequency on the Atlantic side. This latter 

 condition extends south of Cape Horn. 



Temperature has risen uniformly at all places south of 60° S., where the increase 

 amounts to 6°. Elsewhere, within the limits of the area under discussion, the rise is 

 remarkably uniform, being from 3° to 4°. The isotherms present few features of 

 interest, with the exception of a relatively low temperature in from 5 V to 55° S. between 

 the meridians of 65° and 70° W. This appears to be associated with an increase of 

 south-west winds over the above region, a concomitant of the pressure-changes now in 

 progress. 



The cloudiest zone, indicated by the isoneph of 90, is now well south of the 60th 

 parallel, and on the Pacific side reaches to the Antarctic circle. North and south of 

 this a decrease of cloud-amount is observable, the diminution being most marked in the 

 neighbourhood of Staten Island, where it is at its minimum for the year. 



In December, the most marked change in the distribution of pressure is a small but 

 general rise over Antarctic and sub- Antarctic regions. Elsewhere pressure has fallen, 

 but not to any appreciable extent, being most noticeable at Sandy Point, where it 

 amounts to 0*08 inch. A well-defined area of relatively high pressure is shown over 

 Graham's Land (where pressure is at its annual maximum), and in the south-east of 

 the Bellingshausen Sea. To the east and west of this anticyclonic region low- 

 pressure areas are shown. Gradients are slight everywhere, and gale-frequency has 

 greatly diminished. From about 30° W. to east of the meridian of Greenwich, in from 

 50° to 60° S., gales have increased, pointing to a steepening of gradients in this region, 

 south of which, however, there are no data. 



Winds from quarters to the south of west are unusually frequent in the South 

 Orkneys, Tierra del Fuego, Evangelists Island, and the Falklands ; while at the latter 

 station, as well as at South Georgia, south-east and east winds are at their annual 

 maximum, pointing to the effect of the widespread changes of pressure referred to. 



Temperature in this, the midsummer month of the southern hemisphere, has risen 

 most in the Antarctic, where the powerful influence of the midnight sun is asserting 

 itself. The rise is least in the South Orkneys, where cold southerly and south-westerly 

 winds blow with greater frequency than in any other month of the year. 



Cloud- amount has increased over the ocean on the Pacific side of Cape Horn south- 

 ward up to the limit of observation, the maximum for the year being very generally 

 reached in this area. 



While the characteristic features of the various months are as I have described, yet 

 from time to time abnormal conditions prevail. I have selected December 1904 for 

 special study because of the unusual pressure distribution and wind-circulation. 

 Normally, there is at this season an area of relatively high pressure over Graham's Land, 

 with low-pressure systems to the east and west, and an increase of pressure to the north 

 of 58°, with isobars running along parallels of latitude. But in the month under 



