430 



SCIENCE 



[N. S. Vol. XXXIX. No. 1003 



west. Ice on the lakes by diminishing eva- 

 poration reduces the snowfall of the leeward 

 shores. Thus the heaviest snowfall conies 

 early in winter on the east shores in marked 

 contrast with the late winter maximum on 

 the west shores. 



THERMOMETER EXPOSURE 



Dr. W. Koppen in the Meteorologische 

 Zeitschrift, October and November, 1913,^ has 

 presented the results of a long study of ther- 

 mometer exposure in different parts of the 

 world with many shelters. His results are 

 briefly stated below. To determine air tem- 

 perature the thermometer must be sheltered 

 from radiation but not from the air; the air 

 must not travel far between radiators before 

 reaching the thermometer, and the shelter 

 must have low specific heat and be a poor 

 conductor. The English (Stevenson) shelter 

 in the small form of 1883 fulfills the above 

 stipulations very well. But to eliminate the 

 effect of heating by the sun and excessive 

 cooling at night, a screen is necessary. Dr. 

 Koppen proposes a small and simple screen 

 of grass, rushes, brush or palm leaves to be 

 set over the shelter in such a way as to ex- 

 clude sunlight when the sun is more than 20 

 degrees above the horizon. The roof of the 

 shelter should be of this material also. As the 

 small Stevenson shelter is too small for the 

 ordinary thermograph and hygrograph, a com- 

 bined instrument is suggested instead. Since 

 the English shelter is extensively used, these 

 modifications proposed by Dr. Koppen to ob- 

 tain strictly comparable temperature data can 

 be made with facility. 



CHANGES OF CLIMATE 



PROFEgsoR J. W. Gregory, of Great Britain, 

 presented a paper entitled "Is the Earth 

 Drying Up ? " before the Eoyal Geographical 

 Society, December 8, 1913.2 Of the three 



i"Einheitliche Thermometeraufstellung fiir 

 meteorologische Stationen zur Bestimmung der 

 Lufttemperatur und Luf tfeuchtigkeit, " pp. 474- 

 487, 513-523, 1 plate. 



2 Review by " E. G., ' ' Nature, London, Decem- 

 ber 11, 1913, p. 435. 



general views in this matter, the first (Prince 

 Kropotkin) maintains that the earth has a 

 general tendency towards drought; the sec- 

 ond (Professor Ellsworth Huntington) that 

 while there is this general drying the more 

 important changes are pulsatory, and the 

 third (Mr. E. Thirlmere) that climate varies 

 in cycles of 2,000 years or more and that we 

 are now cooling. Professor Gregory put the 

 evidence from different countries on a map. 

 The result shows probable desiccation in his- 

 toric times in Central Asia, Arabia, Mexico 

 and South America; but increased rainfall 

 in the United States of America, Greenland, 

 Sweden, Eoumania and Nigeria. There 

 seems to have been no appreciable change in 

 Palestine, North Africa, China, Australia 

 and by the Caspian Sea. Thus while there 

 seem to have been local variations there has 

 been probably no general change in climate 

 in the historic past. At any rate, no great 

 universal change could be expected without 

 a considerable change in land and water dis- 

 tribution or of the intensity of solar radiation. 



AIR MOVEMENT IN THE CIRRUS LEVEL 



The geophysical institute of the University 

 of Leipzig has recently issued a work by Th. 

 Hesselberg, " Die Luftbewegungen im Cirrus- 

 niveau." ^ From comparison of the tracks of 

 cyclones and anticyclones with the stream 

 lines shown from cirrus observations, the fol- 

 lowing results have been obtained. Cyclones 

 and moving anticyclones move in the same 

 directions as the air in the cirrus level over 

 the center. The velocity of movement of 

 cyclones and anticyclones is in the mean 0.2 

 to 0.4 of the velocity of air in the cirrus level. 

 The relative velocity is smaller the deeper the 

 minimum and the higher the maximum. 



Air movement in the cirrus level seems to 

 be controlled by the pressure and temperature 

 conditions on the earth. The more intense 

 the cyclone or anticyclone and the smaller the 

 horizontal temperature gradient the greater is 

 its effect on the currents above. The disturb- 

 ance which a cyclone makes on the cirrus path 



3 Second Series, Vol. 2, 73 pp., 48 maps, Leipzig, 

 1913. 



