Clayton — Six and Seven Day Weather Periods. 231 



these, however, appear to be multiples of six, or seven days. 

 In the Meteorologische Zeitschrift for February, 1886, p. 49, 

 Magelssen has pointed out a periodicity in the temperature of 

 about 12 days, combined with another of about 50 days. 

 Balfour Stewart claimed the existence of a period of about 24 

 days (Nature, 1879-81). If these periods are arranged in 

 sequence with the three and six day periods, there is found a 

 geometrical progression as follows, 3, 6, 12, 21, 50. 



The present writer has several times found examples in the 

 United States of Periods in the pressure, temperature or rain- 

 fall of about 14, 21, and 30 days (American Meteorological 

 Journal, June, 1885, p. 87 ; and' Feb., 1886, p. 429.) Again 

 there appears a geometrical progression as follows, 3J, 7, 14, 

 21, 29 or 30. 



In this way there appears to be an analogy to the phe- 

 nomena of sound. The six and seven day periods may be con- 

 sidered the primary notes and the periods of 2, 3, 4, 5, 6, etc., 

 times these lengths whose amplitude of oscillation decreases 

 in proportion to their length may be considered as harmonics. 

 The variations in the weather are made up by the variations in 

 intensity of these components. 



The causes of these periodicities are not clear ; but the fact 

 that they have definite and rigid lengths renders it almost cer- 

 tain that they are connected with some physical or astronomical 

 period, or periods. The breaks in the six and seven day periods, 

 and the redistribution of storm tracks correspond so closely with 

 the accepted length of a solar axial rotation as to make it 

 extremely probable that there is a connection between the 

 two. In this case the sun may perhaps be considered in the 

 light of a tuning fork which sets up the periodic oscillations. 

 The same is probably true of the 11 year sunspot period. 



The periodic phase of meteorological phenomena is undoubt- 

 edly complex, and much is yet to be cleared up and solved ; 

 but even the present knowledge can be used with considerable 

 success in forecasting, as demonstrated by a practical test. See 

 the American Meteorological Journal, February, 1886, p. 429. 



