606 PROCEEDINGS OP THE AMERICAN ACADEMY. 



obtained by Dr. Ekholm and Mr. Arrhenius from the thunderstorms 

 observed throughout Sweden in 1880-95. The uusmoothed results give 

 a decided maximum of thunderstorms (50 per cent above the mean) on 

 the third day after the first quarter, and a minimum (34 per cent below 

 the mean) three days before the last quarter. But the plotted curve is 

 irregular and the curve given here is plotted from the results smoothed 

 by a process described in the pamphlet " Ueber den Einfluss des Mondes 

 auf die Polarlichter uiid Gewitter, von Nils Ekholm uiid Svante Arrhe- 

 nius " (Swedish Academy of Science, 1898). No. II. shows the number 

 of lightning strokes which were recorded in Bavaria from 1844-78 as de- 

 termined by E. Wagner for each day of the moon's synodic period (Mete- 

 orologische Zeitschrift, August, 1889). No. III. is from the number 

 of thunderstorms found in Germany by Dr. Koeppen for each quarter of 

 the moon from 1879-83 (Meteorulogische Zeitschrift, January, 1885), 

 A smooth curve is plotted through the numbers ut each quarter. No. 

 IV. is plotted from the number of thunderstorms in Bavaria found by 

 E. Wagner for each day of the synodic period from 1880-88. Before 

 plotting, the numbers were smoothed by taking the mean of each five. 

 No. V. was plotted from the total number of thunderstorms on each day 

 of the period from 1894-98, determined for me by Mr. A. E. Sweetland, 

 The results were reduced to percentages, and smoothed by getting the 

 second mean of each successive two before plotting. The range is from 

 +8 to —12 per cent of the mean. 



The well known meteorologist Luke Howard was much interested in 

 the question as to whether there was a period in the weather correspond- 

 ing to the tropical period of the moon, or to the time of its movement 

 back and forth across the plane of tlie earth's equator. From a careful 

 study of the observations made in the vicinity of Loudon, for the eighteen 

 years from 1815-32, he arrived at the conclusion that the most rain (by 

 measure at the earth's surface) falls in the weeks when the moon is south 

 of the equator and least when it is passing over the equator southward, 

 the full north declination and tlie week during which it is approaching 

 the equator having a mean quantity. " On investigating the connection 

 of rain with thunder he finds that the atmosphere of our climate is sensi- 

 bly more subject to electrical accumulation in the clouds and to the 

 consequent changes when the moon is either south of the equator or 

 returning from that position." From his studies of the air temperature 

 he deduces the following conclusions : " (1) That the pressure of an 

 atmospheric tide which attends the approach of the moon to these lati- 

 tudes, raises the mean temperature 0.35 of a degree. (*2) That the 



