466 



The following figures taken from ' Davis' Elementary Meteorology ' are of interest in this connection. 

 Taking the amount of heat received from the sun in one day at the equinox on the equator as the unit, 

 the amount received on December 21 at the South Pole is l - 284. This is greater than the amount 

 received at the North Pole on June 21st by 0-082, owing to the greater proximity of the sun. So far as'we 

 know, in the North Polar regions the summer temperature rises to the freezing point, and a reason why it 

 should not rise much beyond it has already been given, but in the Antarctic the summer temperature is far 

 below freezing. The reason must, I think, be sought for in the dryness of the air. The question is discussed 

 elsewhere ; it will suffice here to say that the wet bulb readings indicate a relative humidity that may 

 compare favourably with some of the dryest regions of the earth. There can, I think, be no doubt that 

 the presence of carbonic acid and aqueous vapour in the air tends to raise the mean annual temperature 

 of the earth. Indeed, a change in the amount of carbonic acid has been suggested as a likely cause of 

 the large alternations of temperature that geology shows to have occurred. This question has been very 

 fully discussed by Dr. NILS EKHOLM ('Quarterly Journal of the Eoyal Meteorological Society,' Vol. XXVII, 

 p. 1). The amount of carbonic acid is presumably much the same in all parts of the earth that are not 

 near some large city, but the Antarctic regions probably possess the minimum of aqueous vapour. There 

 would, therefore, be very little check to the free radiation of dark heat into space. 



It would almost appear as though this must be the cause of the low temperature, for one cannot 

 suppose that there is any colder part in the neighbourhood from which cold winds can blow, the whole 

 region, except where there is open water, being subject to the same conditions, namely, a snow-covered 

 surface and intense insolation. Neither can it be supposed that the sun has no time to warm the surface 

 of the snow and ice up to the freezing point after the winter's cold, since the months of March to April 

 on the one side and October to November on the other show changes of nearly 20 F. 



There appears to be no source, so to speak, from which the cold of July can be supplied, save that of 

 radiation from the snow, but if the radiation of heat into space is active, the solar radiation should 

 be equally so, and the more capable of raising the temperature to 32 F. and then supplying heat to 

 melt the ice. That the solar insolation is extremely powerful was proved by the fact noted by the 

 members of the expedition, that as soon as a slope of rock became bare, the sun melted the ice and snow 

 near, and a pond was formed below it. This proves what was well known before, that snow is capable 

 of reflecting the solar heat, but unless it be an exception to the common rule, which is hardly credible, 

 this power of reflection implies a low power of radiation. The thermal capacity of the atmosphere as a 

 whole is small, being equivalent to a depth of about 8 feet of water, but it is useless to look for an 

 explanation in this direction, because similar conditions hold in the Arctic regions and do not produce 

 the same effect. There is one other point which must be mentioned not that it is a possible source of 

 cold, but because it has sometimes in the past been fallaciously put forward as such and that is the presence 

 of a current of air descending from the upper and colder layers of the atmosphere. Such a current 

 must, of course, in virtue of its dynamic warming as it experiences a higher pressure, be a source of heat 

 and not of cold, arid were it not that old fallacies die hard it would not be necessary to refer to it, 



Whatever the cause of this low summer temperature may be, the fact is interesting and important, 

 since it throws some light on the question of the glacial epochs of the northern hemisphere, and shows 

 that an intense solar insolation may be so modified by other circumstances that it does not produce the 

 effects which one would naturally expect. 



From the fact that for long periods in each winter the mercury never rose much above F., and 

 yet winds from an equatorial point were frequent, it may be inferred that there was very little open 

 water in the neighbourhood. The absence of fogs leads to the same conclusion. Lower mean 

 temperatures from July to September might therefore have been expected, since in the northern 

 hemisphere, in much lower latitudes, temperatures of - 30 F. and less are not uncommon, and the 

 mean temperature of the southern hemisphere, as a whole, is less than that of the northern. Perhaps 

 an explanation may be sought for in the more active circulation of the southern hemisphere. As soon 

 as the sun has nearly reached the horizon, the radiation of heat into space, intensified by the prevailing 

 dryness, has full play, and since snow is a bad conductor of heat, the only source of heat is the supply 

 by convection through the atmosphere. Owing to the absence of land, the temperature in the belt 



