354 SCIENTIFIC RECORD FOR lbd4. 



any cosmic cause is out of the question. Now that this conclusion has 

 been confirmed by von Bezold by his demonstration of their purely terres- 

 trial cause, and that they occur pretty uniformly distributed through a 

 long interval of time, it seems strange that Koppen should state that the 

 main point of the question has not yet been touched, and should again 

 suggest cosmic explanations. Billwiller's opinion is that there are no 

 facts on record from which we can philosophically conclude that there 

 Siie three definite cold days in May or that there is any problem here 

 to be investigated. [In other words, this problem is to the German 

 what the problem of the equinoctial storm is to the American. What- 

 ever storm happens to occur within a week or two of the 21st of March 

 or September is called the "equinoctial storm," and we frequently find 

 some one at work on the problem, "Why are storms especially aj)t to 

 occur on the equinoctial day?"] {Z. 0. G. M., xix, p. 245.) 



315. Dr. W. Koppen, in reply to Billwiller's remarks, states decidedly | 

 that he is not a believer in the three cold days of May, nor in their ^ 

 explanation by cosmic causes. The essence of the problem seems to him 

 to lie in the following questions : 



1. Is there really iiresent that relative maximum tendency to cold 

 days which, according to many, especially the older observations and 

 according to the investigations of von Bezold, apparently exists during 

 the third pentade of May ? 



2. If this is the case, how shall the date be exactly determined ? 

 Even if the first question should be denied, it would still remain of 



interest to show why the tendency to a south and a southeast gradient — 

 that is, to a northeast wind — should be so decided in May, and should 

 also not exist in June, where the excess of temperature of the continents 

 above the sea remains the same while north and northeast gradients 

 jjrevail. He shows that this may be due to the heating of distant lands, 

 and remarks that also the studies of Dr. Krankenhagen on the baro- 

 metric phenomena attending the cold period in June combine to show 

 that in severely judging the belief in the definite character of special 

 days we may have gone too far. 



316. Buys-Ballot writes expressing his entire agreement with Pro- 

 fessor Billwiller. He states that every month has its cold days, and May 

 least of all, and suggests a method of investigation which he is about 

 carrying on. In a parenthesis he exclaims, " Shame, that in America 

 climatology is so entirely lost sight of!" {Z. 0. G. M., xix, p. 320.) 



317. G. Hellmann, in a study of the annual change of temperature in 

 Northern Germany, utilizes the averages by pentades for thirty five 

 years ; he finds a decided retrogression or cold period about the middle 

 of June for Breslau. The cold days of May vary so much as to their 

 dates that they do not show in the averages of thirty-five years, while 

 the cold days of June are well marked. Another retrogression, but in 

 this case warm days, occur iu the last week of September, [Z. 0, G, M.^ 

 XIX, p. 384.) 



