Anticyclones and S.A. Weather. 



67 



Appendix VI. 

 Royal Alfred Observatory, Mauritius. 



Barometric Pressure, Departure from Average in each Month of 



the Year. 



Month. 



January 

 February- 

 March 

 April... 

 May ... 

 June ... 

 July ... 

 August 

 September 

 October 

 November 

 December 



1899- 

 inch. 



1900. 

 inch. 



-•027 

 -■032 

 -•019 

 -•003 

 -•005 

 -•004 

 + •067 



+ •055 

 + •018 

 + •003 

 -•010 

 -(-•032 



+ •056 

 + •030 

 -•003 

 -•008 

 -•009 



-•013 

 + •030 

 + •021 

 + •011 

 + •050 

 + •018 

 + •070 



1903- 

 inch. 



1904. 

 inch. 



Remarks. 



The recovery from a 

 negative wave which 

 culminated in December, 



1902, persisted throughout 



1903, until October, when 

 pressure returned to the 

 normal. This wave was 

 the greatest on record, the 

 defect in pressure for 18 

 months being 0'5I9 in. 

 The next greatest on re- 

 cord was from Aug. 1 875 

 to Feb. 1876, the total 

 defect being 0*399 in. 



From Oct. 1903 to the 

 middle of 1904, pressure 

 increased steadily rela- 

 tively to the normal. 



Note. — Barometric pressure. — The Report for 1904 says, ' The pressure 

 abnormalities since the end of the year 1901 have been remarkable both 

 for amplitude and regularity. The curve fell generally from + 0'042-in. 

 in September, 1901 to -0'090-in. in December, 1902; rose to + 0"062-in. 

 in June, 1904, and then decreased to -0"036-in. in January, 1905.' 

 Viewed in connection with a progressive movement of the Australian 

 Anticyclone to and from South Africa in each year, an explanation of 

 such abnormalities, or ' negative and positive waves ' is given by the theory 

 that has been advanced. The anticyclone does not follow the same path 

 to and fro each year, nor does it pass Mauritius at exactly the same time. 

 This will affect the barometer in the way indicated by these so-called 

 ' waves.' The rainfall is very significant during the period 1880 to 1903, 

 and points to a varying influence from a high pressure system, which is 

 ever altering its relative position with respect to Mauritius, while its 

 movements continue to be progressive and regular. The drought of 1880 

 was associated with an exceptionally well marked positive pressure wave, 

 and that of 1885-6 with the recovery of pressure after a feeble negative 

 wave, i.e., in 1880 the anticyclonic system was near Mauritius at the time 

 of the rains and influenced the fall, while in 1885-6 it was returning to its 

 normal path after a deviation which allowed the rain-bearing system to 

 come in. The drought of 1889-90 was synchronous with a feeble negative 

 pressure wave, following a well marked positive wave, while that of 1893 

 was synchronous with a well marked positive pressure wave between 

 two equally well marked negative waves. From 1896 to 1898 the rain- 

 fall abnormality curve was slowly recovering from a steep minimum, 

 while the pressure curve was falling steadily. What more suggestive 

 record could there be of a gradual retrocession of the high pressure 



