469 

 RADIATION Thermometers. 



The actual maxima are in no way exceptional : a glance at the Climatological Tables published monthly 

 by Dr. MILL in SYMONS' ' Meteorological Magazine ' will show that higher values are by no means 

 uncommon in various parts of the world, but if instead of taking the actual reading we consider the 

 difference between the maximum temperature of the day and the maximum recorded by the black bulb 

 thermometer, we find an amount that it would be very hard to match. Thus on December 21, the day 

 which gives the absolute maximum, 1 54 F., the mean temperature only reached 1 7 8, and the maximum 

 24" "2, and during December, 1902, when the average was 123", the mean temperature of the air was only 

 23 1, the difference for 31 consecutive days reaching an average of just 100 F. The following month, 

 January, 1903, has not quite so great an average difference, but on one day only during this month did 

 the radiation thermometer fail to reach a temperature of 100 F. 



It has been previously stated that the insolation during December and January at the South Pole is very 

 great, but that is because the sun is continuously above the horizon. If the amount of heat received on a 

 unit of surface during the midday hour be taken instead of the amount received during the 24 hours and 

 it is this which influences the maxima readings and if this amount be compared with the corresponding 

 amount received at the equator, the comparison, in so far as magnitude is concerned, is entirely in favour 

 of the equatorial region. At the South Pole the insolation on December 21 is 0'4 of that of a place 

 where the sun is in the zenith ; at the Winter Quarters of the " Discovery " at midday it would be - 58, a 

 little over half. But the solar rays have also to pass through nearly twice the quantity of air, and were 

 this air at all impervious, they would lose a considerable part of their heating effect. It follows that these 

 black bulb readings show that the air of the Antarctic regions offers very little obstacle to solar radiation, 

 and one can hardly doubt that the cause of this permeability must be the absence of aqueous vapour. 

 Inasmuch, too, as the radiation maxima are high in the summer without exception, we must assume that 

 no thick sheet of clouds ever remained for long over this station. It seems likely, therefore, that the 

 Antarctic anticyclone is very active, and that there is a general and extensive settling down of air. 

 Otherwise the dryness could not be maintained, for, the whole surface being ice, snow, or water, and 

 therefore capable of giving off aqueous vapour, the air would of necessity soon be filled with moisture, 

 since evaporation from the snow would soon saturate the surface layers and the vapour would diffuse 

 upwards. 



CAPE AKMITAGE. 



In addition to the regular observations made at the ship, observations of the temperature were made at 

 Cape Armitage once at least on most days in the winter. No precise time was adhered to, but the 



