E.. H. Clayton — Seven Bay Weather Period. 



15 



the frequency of barometric minima except from September 

 to November. 



In South America only two maxima appear, but the positions 

 of the maxima tend to vary simultaneously with those in the 

 northern hemisphere, and thus add some support to the hypoth- 

 esis that the causes of variation in the period are cosmical and 

 not seasonal. 



As a further investigation the number of barometric maxima 

 occurring on each day of the period was counted for all 

 the above mentioned stations in Europe and the United States. 

 The results show, with only one or two slight exceptions, the 

 greatest frequency of barometric maxima about half way 

 between the barometric minima, and when the two are plotted 

 together they show similar, but reversed, curves. Since this 

 result is perhaps what was naturally to be expected, the tabular 

 matter is omitted here, but the results for Cheyenne, Chicago, 

 and Blue Hill are plotted in diagram 1 by means of dotted 

 lines over the continuous curves which show the frequency of 

 barometric minima. 



To ascertain to w^hat extent the period would show itself in 

 short intervals, the periods were separated into groups of eleven 

 periods occupying about eleven weeks each, and the barometer 

 observations taken three times a day at Blue Hill Observatory 

 were averaged for each eight hours of the period from 1890 to 

 1895. The results for 1890 were the most marked and are 

 given below, though I think the results for each year suffi- 

 ciently confirm the existence of the period. The dates in this 

 table are the dates of the beginning of each group. 



Table V. 



Day 



1 



2 



3 



4 



5 



6 



7 



Bar. 29-+ inch 

















Jan. 3 



35 42 45 



49 52 49 



43 33 29 



24 27 31 



31 29 28 



33 32 27 



18 20 26 



Mar. 16 



24 32 36 



38 35 30 



22 20 22 



24 27 31 



30 26 28 



31 29 27 



23 22 24 



June 4 



29 30 31 



29 29 29 



32 33 36 



39 41 42 



41 39 37 



34 29 28 



25 23 27 



Aug. 23 



27 29 32 



34 31 28 



38 41 42 



41 29 28 



31 32 31 



26 20 17 



16 19 22 



Oct. 6 _ 



12 12 12 



19 20 28 



3*7 41 42 



32 22 18 



19 26 31 



27 21 15 



09 12 14 



It will be seen from Table Y that the chief minimum 

 remained persistent on the seventh day. The secondary mini- 

 mum moved forward from the beginning of the fourth day in 

 winter to the end of the second day in the period in summer, and 

 toward the end of summer showed a double minimum, one on 

 the second, and the other on the fourth day. In autumn and 

 early winter the minima are again on the fourth and the seventh 



