METEOROLOGY AND OTHER SCIENCES 737 



At any rate, the previously made calculations seem to indicate that 

 the order of magnitude of the possible variations is about as large as 

 the corresponding observations of the geologists. 



Here, then, the sciences of meteorology, physics, likewise geology 

 or its companion sciences, botany and zoology, work together. Meteor- 

 ology has, of course, not only to consider the present condition 

 of the atmosphere, but also the past, and, so far as possible, its 

 future condition. 



I have recently carried out a calculation with respect to the sun's 

 corona which shows that the temperature of the corona, which may 

 be regarded as locating the highest atmosphere of the sun, may be 

 considered as due solely to radiation from the sun. Although the 

 radiation there is incomparably greater than in the highest layers 

 of the earth's atmosphere, it is yet probable that here the tem- 

 perature of the floating dust-particles especially those which 

 through their negative charge serve in the explanation of the polar 

 lights is chiefly determined by radiation, from the sun, and 

 from the earth. The temperature of these dust-particles on the side 

 of the earth facing the sun lies between 40 C. and 60 C., and upon 

 the dark side between 30 C. and 40 C., in temperate zones. 

 This temperature may be regarded as approximately that of the 

 highest layers of the atmosphere. It is, in any case,- much higher 

 than formerly supposed. 



We have now penetrated to a certain extent into the domain 

 where meteorology and the modern theory of electrons come into 

 contact. C. T. R. Wilson showed that the negative electrons of the 

 air serve to a greater degree than the positive electrons as condensa- 

 tion nuclei in the precipitation of water- vapor. A consequence of this 

 is that generally the precipitation is negatively electrically charged, 

 a fact recognized by Franklin, and later confirmed by Elster and 

 Geitel. Furthermore, since the ionization of the air increases with 

 the altitude, it is reasonable to expect that the clouds will be more 

 strongly charged the greater the height at which they are formed. 

 This conclusion is confirmed by experience. Clouds which are 

 formed at low altitudes are, for the most part, only weakly electrified; 

 and the peculiar thunder-clouds, which are more strongly charged 

 the higher the rising air-currents upon whose upper side they are 

 formed extend, originate at great altitudes. Such powerful air- 

 currents occur to the best advantage over the land at the hottest 

 time of the year, and upon this fact depends the distribution of 

 thunder-storms with reference to the time of year. With respect 

 to the warm air-currents over the sea, the conditions are just the 

 reverse. Since the excess of temperature of the sea over its sur- 

 roundings is greatest in winter, the fact of the maximum occurrence 

 of oceanic thunder-storms in winter is explained. 



