CLAYTON. — PERIODICITY IN THE WEATHER. 607 



rarefaction iiiider the moon in north declination lowers the temperature 

 0.13 of a degree. (3) That the northerly swell following tlie moon as 

 she recedes to the south further cools the air 0.18 of a degree. (4) That 

 this cold continues while the moon is away south, reducing the mean 

 temperature yet lower by 0.04 of a degree." (Papers on Meteorology, 

 etc., by Luke Howard, F. R. S., London, 1854, p. 44.) In showing 

 the greatest number of thunderstorms when the moon is south, Howard's 

 results agree with the later ones of Dr. Ekholm and Arrhenius and of 

 Mr. Sweetland and myself. M. P. Garrigou Lagrange of the Obser- 

 vatoire Physique et Meteorologique, at Limoges, France, investigated 

 the relation between the moon's change in declination and the change in 

 the pressure of the atmosphere over the northern hemisphere, using for 

 this purpose the international observations of 1882-83. His conclusions 

 as communicated to the Societe Meteorologique de France are: — (1) In 

 the atmosphere of the northern hemisphere there exists an oscillation 

 from one side to the other of about the 30th parallel synchronous with the 

 movement of the moon in declination and of such a nature that when 

 the moon is north the pressure is lower below the 30th parallel and higher 

 above it, and inversely when the moon is south. (2) The gradients 

 show correlative moditications. The barometric slope from latitude 30° 

 toward the south and toward the north is alternately raised and lowered, 

 being steepest below 30° when the moon is north and less steep above 

 30° and inversely when the moon is south. (3) These differences in the 

 pressure and the gradients increase in proportion as one advances toward 

 the pole, at least as far as the 70th parallel. (4) These movements are 

 superposed on the more general movements which they strengthen or 

 weaken as they are in the same or in a contrary direction. 



In 1894, Dr. Nils Ekholm and Svante Arrhenius published an investi- 

 gation on the relation between the electrical potential of the air and the 

 position of the moon in declination. (Ueber den Einfluss des Mondes au£ 

 den Electrischen Zustand der Erde, Bihang till K. Svenska Vet. Akad. 

 Handlingar, Band XIX., Afd. I., No. 8, Stockholm, 1894.) They found 

 that in the northern hemisphere the difference in potential between the 

 earth and air was greatest when the moon was in southern declination 

 while in the southern hemisphere it was greatest when the moon was in 

 northern declination, the variations being 20 per cent or more above 

 and below the mean. In Plate IV. the curves marked "Atmospheric 

 Electricity " show the results for Cape Horn and Cape Thordsen (Spitz- 

 bergen). The curve marked " S. Hemisphere" is for Cape Horn; the 

 one marked " N. Hemisphere" is for Cape Thordsen. The explanation 



