120 MR ROBERT C. MOSSMAN ON THE METEOROLOGY OF 



40° to 70° S. the mean monthly and annual values of barometric pressure, air tempera- 

 ture, amount of cloud, rainfall, wind velocity, relative humidity, and percentage 

 frequency of wind. In their preparation I have used all the reliable material, but have 

 discarded returns from stations the observations from which did not inspire one with 

 confidence. Thus the barometric pressure is not given for Evangelists Island, as the 

 readings are obviously in error. The data from Tierra del Fuega have been carefully 

 sifted, especially with reference to mean barometric pressure. Particular trouble was 

 taken to obtain good barometric means for the region around Cape Horn, which is of 

 great importance as a general control on the isobars. With regard to temperature 

 observations, Table II., the means given are those observed, but in plotting the values 

 for drawing the isotherms the values were corrected to sea-level by adding 1*0° F. for 

 every 300 feet. As only two stations exceed 150 feet, these corrections were small. 

 No correction was made to bring the values to the mean of the 24 hours, as, except New 

 Year's Island, which was specially treated, the means of the tri- daily observations give a 

 very close approximation to the mean of the 24-hourly values. As regards New Year's 

 Island, the hours of observation were 7, 8, 10 a.m., and 1, 4, 7, and 10 p.m., and the 

 mean of these was brought to the mean of the 24-hourly values by adopting the values 

 obtained from a reduction of the thermograph records at the adjacent station of Staten 

 Island. The monthly corrections, which are all minus, are as follows : — 



Jan. Feb. Mar. April. May. June. July. Aug. Sept. Oct. Nov. Dec. Year. 

 09 0°8 0°7 0-6 0°5 0°3 01 0°2 0°4 0°6 0°7 0°8 0°45 



The mean monthly and annual amount of cloud is given in Table III. 



Table IV. gives the mean monthly and annual rainfall. As regards Sandy Point and 

 Dungeness, the values appear to be too low. This is due in the former instance to the 

 rain gauge being at some distance above the ground. Owing to the frequency of drifting 

 snow at the South Orkneys, the precipitation there cannot be given, but, on a review of 

 the whole existing material, I am inclined to assign a much larger precipitation to this 

 region than that given in my report.* I think about 25 to 27 inches is the probable 

 annual rainfall, with a maximum in summer. As Laurie Island is on the lee side of the 

 South Orkney group with reference to the prevailing westerly winds, it is probable that 

 the precipitation is much greater on the neighbouring Coronation Island to the west. 



Table V. gives the mean hourly velocity in miles for the first six, and the mean 

 force of the wind on the Beaufort scale 0-12, for the last seven stations. 



Table VI. gives the mean relative humidity, deduced in most cases from readings of 

 the dry and wet bulb thermometer, but at Wandel Island the records are from a Richard 

 Hair hygrograph. 



Table VII., showing the mean monthly and annual percentage frequency of the 

 winds, has involved much labour, as the data for the South Orkneys, South Georgia, 

 Evangelists Island, and Dungeness were either wholly or partially unreduced. In 

 every case the values have been reduced to eight points, and the numerical results 



* Scientific Results of the " Scotia" : Meteorology, p. 274. 



