﻿342 Mr. J. K. Laughton on Barometric Differences 



continuous range of mountains on the south, there seems abso- 

 lutely no reason, so far as temperature is concerned, why the area 

 of low pressure should not be in Germany or Russia instead of 

 in Siberia*. But in other respects there is a wide difference 

 between the summer climate of Central Europe and Eastern 

 Asia. The rainfall, which throughout Russia is trifling, and on 

 the plains of Siberia is scanty, is very great on the mountain- 

 slopes to the south and east. " In the neighbourhood of Rid- 

 dersk in the Altai Mountains, the dew falls so heavily that the 

 dress of the horseman is completely saturated when riding 

 through the high grass, while in the sombre forests of the north- 

 western Altai, called locally Taigi, the atmosphere is still more 

 humid, and rain during some summers falls incessantly"-]-- Such 

 rain acts here in the same way as the still heavier rain acts south 

 of the Himalayas. Wherever aqueous vapour is largely with- 

 drawn from the air, the elastic force must be reduced, even 

 though the reduction may not always be so great as to affect the 

 barometer; and in this instance, since we know that in July the 

 aqueous vapour at Barnaul has a mean tension of "43 of an inch, 

 that the air in Thibet is excessively dry, and that on the Thian 

 Shan Mountains dew and rain are almost unknown even during 

 summers which on the Altai are unusually wet J, we must admit 

 that the northerly and north-westerly wind which brings the 

 vapour into Siberia is entirely deprived of it as it passes out. 



But whilst the low barometer of Hindostan, of the Doldrums, 

 or of Siberia may thus be explained by the free and excessive 

 condensation of aqueous vapour, it is impossible in any similar 

 manner to explain the low barometer of the Antarctic, a district 

 which offers a decisive contradiction to every law which meteo- 

 rologists have proposed : it is an area of extreme cold, yet the 

 barometer is not high ; it is an area of low pressure, but the pre- 

 vailing winds do not blow towards it. What the actual height 

 of the barometer or thermometer may be within the icy region 

 we have no means of knowing; but it may fairly be supposed 

 that they are both very low; and it is quite certain that the 

 pressure diminishes steadily from the parallel of 50° southwards, 

 until barriers of ice hitherto impassable put an end to our ob- 

 servations. 



The enormous quantity of snow which overlies the ice and 

 land attests the occasional presence and condensation of aqueous 

 vapour in the air ; but the temperature in the higher latitudes 

 diminishes very gradually, and the tension of the vapour in such 

 air as is swept from warmer seas into the icy regions must be so 



* Buchan, ' Handy Book/ p. 40, plate 4. See also ' Nature,' vol. iii. 

 p. 76. 



t Journ. of the Roy. Geog. Soc. vol. xxxv. p. 227. + Ibid, in he. cit. 



