xxxviii GENERAL SUMMARY OF SCIENTIFIC AND 



rents of air set in converging toward this area ; finally, if among 

 these currents there rushes in a strong southwest or west-southwest 

 current of air saturated with moisture," this furnishes the required 

 abundance of vapor, whose rapid condensation gives out the heat 

 required to form and maintain a cyclone, instead of the small torna- 

 does that would otherwise be the only result. 



In reference to the relation between solar radiation and terrestrial 

 meteorology, Blanford remarks that in India both the annual and 

 diurnal changes in temperature are the reverse of the changes in hu- 

 midity; it would therefore seem that throughout the world, since 

 there is more water than land surface, the principal effect of an in- 

 crease in the temperature of the sun would be to increase the quan- 

 tity of moisture in our atmosphere, and to diminish the temperature 

 of the air at the immediate surface of the earth. 



Plants states that he has observed certain effects that go to show 

 that the formation of hail is due to an electric discharge of low ten- 

 sion accompanied by a gyratory movement of the electrified particles 

 of ice. 



Gronemann has published additional develojDments of his theory 

 of the origin and nature of the aurora, which is that it is an electric 

 discharge among particles of cosmic dust, clouds of which are en- 

 countered by the earth in its annual course around the sun. He 

 finds the explanation of the geographical distribution of the greatest 

 auroral frequency in a zone lying between the parallels of 50 and 

 70 of north latitude to consist in the relation between the position 

 of the earth's axis and the orbits pursued by the cosmic dust. Ac- 

 cording to this theory there may be periodical auroras one of 

 which may possibly recur on the 4th of February. 



Fritz has compared the frequency of auroras, as recorded in his 

 great catalogue, with Wolf's observations of the sun-spots. He finds 

 that the most important auroras agree accurately with the minima 

 of sun-spots, and that the great aurora period of fifty-five and a half 

 years also agrees with five of Wolf 's sun-spot periods : he even thinks 

 it probable that a still longer period of two hundred and twenty- 

 two years may be detected in the records of the auroras. 



Buys Ballot and Wild have published extensive researches upon 

 the distribution of atmospheric moisture or relative humidity in Eu- 

 rope. The former finds the data sutRciently extensive to justify the 

 formation of monthly means and corresponding deviations from the 

 normal values ; he also deduces the influence of altitude above sea- 

 level, and of latitude, longitude, and the neighborhood of the ocean, 



Hann has published an essay on the climate of the Punjab. 

 Among the many interesting items we note that the average range 

 of temperature in a day is from 1G to 20 Centigrade at the three 

 stations where observations have been made for several years ; the 

 actual temperatures averaged 33 Centigrade in June, and 10 Centi- 



