Clayton — Six and Seven Day Weather Periods. 225 



than could be attributed to chance. It was further shown 

 that intervals of six, or three days, would prevail for awhile 

 and then the sequence would break, and intervals of seven, or 

 three and a half, days would follow. Furthermore, it was 

 found that the changes from intervals of one length to that of 

 another were separated by intervals of twenty-seven days, or 

 some multiple of this number, a period which agrees very 

 closely with the length of a solar rotation. 



For a further study of these periodicities, Mr. Fergusson, 

 the assistant observer at Blue Hill Observatory, furnished the 

 writer with the dates and hours of all the barometric minima 

 recorded by the barograph at the Observatory since its estab- 

 lishment in 1885. 



In this data were found many instances of six and seven day 

 periodicities lasting several weeks, and sufficiently striking to 

 be easily recognized. A few of these are here given as illus- 

 trations : 



The Dates and Hours of occurrence of barometric minima at Blue Hill Observatory — 



Ion. 71° W., lat. 4.2° N. 



Showing 7 day intervals. 



April 6, 

 " 13, 

 " 22, 



" 28, 



5, 

 13, 

 20. 



May 



6 p. ii. 



5 p. M. 



2 A. M. 

 2 P. M. 



4 P. M. 

 2 P. M. 



5 P. M. 



7 + 



June 



27, 11 p.m. ' 



3, 1 P. M. _ 



10, 4p.m. 

 17, 11 p. M. n 



July 



3 p. M. 

 3 A. M. 



Interval. 

 cl. hr. 



1 

 33 



— 12 

 + 2 

 + 22 

 + 3 

 + 6 

 -10 

 -3 

 + 7 

 + 40 

 -12 



Oct. 2, 

 " 8, 

 " 17, 

 " 24, 

 " 31, 



Nov. 7, 

 " 15, 

 " 22, 

 " 29, 



Dec. 6, 

 " 14, 

 " 21, 



Interval, 

 d. hr. 



4 A. M. 

 1 P. M. 

 3 P. M. 



1 1 A. M. 



7 A. M. 

 1 A. M. 



8 P. M. 



5 A. M. 



3 P. M. 

 5 A. M. 

 1 A. M. 



4 P. M. 



7 



-15 



7 



+ 50 



7 



— 4 



7 



—4 



7 



— 6 



7 



+ 43 



7 



-15 



7 



+ 10 



7 



-10 



7 



+ 20 



7 



+ 15 



1891. 

 April 12 

 " 19 



Interval, 

 cl. hr. 



Mav 



28, 

 4, 



June 



4 A. M. 



3 P. M. 

 1 P. M. 



4 P. M. 

 11, 5 P. M. 



18, 4 p. M. 



26, 4 P. M. 

 2, 4 p. m* 

 9, 5 P. M. 



16, 5 p. M. 



23, 5 A. M. 



7 



+ 11 



7 



+ 46 



7 



— 21 



7 



+ 1 



7 



— 1 



7 



+ 24 



7 



+ 



7 



+ 1 



7 



+ 



7 



-12 



July 



8, 3 p. M. 

 15*, 3 p. M. 



Means, 



Mean Departure, 



7 + 



1886. 



Oct. 



<< .18, 

 " 24, 

 " 31, 

 Nov. 7, 

 " 13, 



Dec. 



6, 5 p. M. 



12, 11 P. M. 



3 A. M. 



4 A. M. 

 2 P. M. 

 6 A. M. 

 4 P. M. 

 2 P. M. 



2 P. M. 

 1 A. M. 

 4 P. M. 



3 A. M. 



6-3 



±13 



Interval. 

 cl. hr. 



18, 

 25, 



1, 



7, 

 14, 



6 



+ 6 



6 



— 4 



6 



+ 1 



6 



+ 34 



6 



+ 16 



6 



+ 10 



6 



+ 22 



6 



-31 



6 



— 20 



6 



+ 15 



6 



+ 11 



7 +7-5 

 ±18 



Showing 6 day intervals. 



Interval. 

 1887. d. hr. 



Jan. 6, 7 A. M. „ 



" 12, 1 p. m. £ 



" 17, 9 p. M. ° 



" 24, 3 p. M. £ 



" 30, 9 P. M. ^ 

 Feb. 6, 6 p. m. p 



" 11, 8 p. M. £ 



" 18, 9 P. M. !! 



" 24, 2P.M.„ * 

 March 2, 7 P. M. ° + 



7 +17 

 7 +17 



7 +0 

 7 + 6-4 

 ±11 



+ 16 



— 16 



+ 18 

 + 6 

 + 21 



— 22 

 + 25 



7 



1891 

 Jan 



Feb. 



11, 



20, 



25, 



1, 



8, 



13. 



21, 



" 26, 



March 4, 



Means, 



Mean Departure, 



+ 5-3 



±14 



6 +3-8 

 ±13 



1 P. M. 



4 P. M. 

 8 A. M. 



5 A. M. 



1 A. M. 



2 P. M. 

 2 A. M. 



11 P. M. 



6 A. M. 

 10, 1 A. M. 

 16, 3 P. M. 



22, 3 A. M. 

 29, 4 a. M. 



Interval. 

 d. hr. 



6 +3 

 6 -32 

 6 +21 



6+20 

 6 —11 

 6 +36 

 6 -3 

 6 —17 

 6 -5 

 6+14 

 6 —12 

 6 +25 



6 +3-3 

 ±16 



Am. Jour. Sci.— Third Series, Vol. XLVII, No. 279. 

 15 



-March, 1894. 



