174 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. JO 



These smoothed curves must therefore, it is to be expected, give 

 best the longer periods of eleven years and upwards. For these 

 he finds a well marked agreement between the curves for sun spots, 

 etc., and those for air pressure at St. Petersburg, but less marked 

 for the curves for other stations in more southerly latitudes in 

 Europe. The air pressure variatio'ns in St. Petersburg in the eleven- 

 year period go in the same way as the variations in sun spots, mag- 

 netic variations and Northern Lights and there is shown a tendency 

 to the same direct agreement at several of the other stations. 



Dr. Brask in Batavia (1910) has determined the variations in air 

 pressure and temperature in Batavia for the period 1866 to 1909 

 and finds in both a complete agreement, with a well-marked period 

 of about three and one-half years. The curves for pressure and 

 temperature are completely similar. Variations in the temperature 

 occur about six months after the corresponding variations in the 

 air pressure. The curve for the air pressure difiference between 

 Batavia and Fort Darwin is similar to the air pressure curve for 

 Batavia, only that it runs oppositely. The short period is, as he 

 himself notes, the same which the two Lockyers have found, but 

 from his curves it appears that the period is best defined as having 

 a length of about three years only. 



VARIATIONS IN WIND AND SUN SPOTS 



As we have seen that the air pressure varies with the solar 

 activity, it should be expected that the winds also vary thus. In 

 the year 1872, Meldrum, the Director of the Observatory at 

 Mauritius, noted that the cyclones in the Indian Ocean between the 

 equator and 25° south latitude varied in number and intensity with 

 the sun spots. He found that in three sun spots periods between 

 1847 and 1 87 1 on the average seventeen cyclones in three years 

 occurred in the neighborhood of the sun spot maximum, while near 

 sun spot minimum in the same number of years only half as many 

 cyclones occurred, or from eight to nine. 



Shortly after this Poey showed that the cyclones in the Antilles 

 have a similar periodicity. For the period of time from 1750 to 

 1873 ^^ found that the maximum of cyclones occurred about one 

 year after the maximum of sun spots, while the minimum of cyclones 

 occurred about one year before the minimum of sun spots. The 

 most decisive proof of the correctness of Meldrum's observations 

 is furnished by the fact that the list of shipping losses of the marine 

 insurance companies shows a similar variation to his assumed 



