600 PROCEEDINGS OF THE AMERICAN ACADEMY. 



as is found to be the case. Again, if during sunspot maxima there 

 should be an increase in atmospheric pressure over the Mid-Atlantic, 

 there would be an excess of soutliwest winds over the British Isles 

 during this time. Since winds in blowing over mountain chains have 

 their moisture condensed, and descend on the other side dry, the above 

 conditions might result during a sunspot maximum in an excess of 

 moisture on one side of a mountain chain and a deficiency on another. 

 Hence, in an area as small as Scotland, opposite weather conditions in 

 different places during the sunspot cycle do not necessarily disprove the 

 existence of the cycle. The results of various investigators from vari- 

 ous parts of the world need to be gathered and carefully considered from 

 numerous standpoints, before the weather cycle can be said to be dis- 

 proved, or before all the phenomena can obtain rational explanation as a 

 result of the cycle. 



Next to the sun, the heavenly body which has obtained most attention 

 as a probable cause of weather cycles has been the moon. A popular 

 belief in the influence of the moon on the weather is older than history, 

 and exists in full vigor to-day. The earlier meteorologists, attracted by 

 this general belief, devoted much time to investigating the question of 

 the relation of weather to the moon's position. Considerable data of vari- 

 ous kinds were accumulated, to which full references are found in Van 

 Bebber's Handbuch der Witterungskunde. The results given in most 

 detail were plotted by Van Bebber, and are here reproduced in Plate I. 

 from traces made with a pantograph. Curve I. was j)lotted from the mean 

 atmospheric pressure at Paris for each day of the synodic peiiod of the 

 moon, as obtained by Eugene Bouvard for the twenty-three years 1810- 

 32. Curves II. and III. are the means of the atmospheric pressure at 

 Carlsruhe and Strassl)urg for each day of the synodic period of the moon, 

 as obtained by O. Eisenlohr for the years 1810-21 and 1806-32, respect- 

 ively. The three curves are in close agreement, showing a minimum 

 pressure about midway between the first (juarter and full moon and a 

 maximum near the last quarter. Curves IV., V., and VI. show the 

 number of rainy days at Paris, Carlsruhe, and Strassburg for each day 

 of the synodic period as worked out by Bouvard and Eisenlohr for the 

 intervals given above. These curves are alike, and show a maximum 

 frequency of rainy days at the time of the minimum of pressure. Curves 

 VII. and VIII. show the number of clear days at Vigevano and Krakau 

 for each day of the synodic period as obtained for the first place by 

 Schiaparelli for the interval 1827-64 and for the second place by Wierz- 

 bicki for the interval 1826-40. The curve for Vigevano shows the 



