224 



NA TURE 



[January 8, 1903 



THE SIMILARITY OF THE SHORT-PERIOD 

 BAROMETRIC PRESSURE VARIATIONS 

 OVER LARGE AREAS. 

 T N an earlier number of this Journal (vol. lxvi. p. 248, 

 ■*■ July 10, 1902), an account was given of the great 

 similarity of curves representing many solar and meteoro- 



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Fig. 



-In this and all the *ui'sequem ligures, the coiniuuous and broken vertical lines 

 repiesent the epochs of sunspot maxima and minima respectively. 



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BOMBAY »• 

 (INDIA ) i, ,„» 



logical phenomena, 1 and it was suggested that their 

 close accordance indicated, not only the intimate relation 

 between solar and meteorological changes, but the im- 

 portance of the short-period (three to four years) vari- 

 ations common to them all. The variations 

 of solar activity, as indicated by the greater 

 or less number of spots or prominences or by 

 the changes of latitude of the former, were 

 suggested to have such an action on the 

 atmospheric pressure on the earth's surface 

 that when one place recorded an excess, 

 another, nearly antipodal as regards position, 

 showed a deficiency of pressure. Thus the 

 regions specially referred to were those of 

 India and that about Cordoba, in South 

 America. 



This reversal of conditions, extreme high 

 pressure in one place and low pressure in 

 another at the same moment of time, inde- 

 pendent of the yearly or seasonal change, a 

 fact which has since been corroborated by an- 

 other investigator, as will be seen further on, 

 can be well seen by examining two pressure 

 curves such as those of Bombay and Cordoba 

 (Fig. 1) ; in each case, the mean pressure for 

 the same months has been used. 



In the paper already referred to, it was 

 further pointed out that just as the pressure 

 variations of Bombay were typical of the 

 whole of India, so were those of Oxford 

 (England) or Valencia (Ireland) for western 

 Europe. 



With these facts in view, it was important, 

 therefore, to investigate the extent of regions 

 having similar pressure variations, and in the 

 first instance to restrict the inquiry to those 

 areas surrounding India and Cordoba. The 

 results of such a barometric survey were com- 

 municated to the Royal Society last October, - 

 and it is the purpose of the present article to 

 state the results which have been obtained. 



It may, however, first be mentioned that the 

 monthly means of the pressure variations for 

 each station were divided, as in the previous 

 article, into two periods, namely, those 



1 " On Some Phenomena which Suggest a Short Period 

 of Solar and Meteorological Changes," by Sir Norman 

 Lockyer. K.C.B., F.R.S., and William J. S. Lockyer, M.A., Ph.D., 

 F.R.A.S. (Roy. Soc. Proc., vol. l.\x. p. 500). [Received June 14, read 

 June iq, IC02.] 



- " On the Similarity of the Short-Period Pressure Variation over Large 

 Areas," by Sir Norman Lockyer, KC IS., F.R.S., and William J. S 

 Lockyer, M.A., Ph.D., F.R.A.S. (Roy. Soc. Proc, vol. lxxi.). [Received 

 October 18, read December 4, 1902. J 



NO. 1732, VOL. 6/] 



months in which the pressures are above and those in 

 which they are below the normal, the normal being the 

 mean pressure for the whole period under investigation 

 in each locality. 



Thus, for instance, to take the cases of Bombay and 

 Cordoba, the former has its high-pressure months from 

 April to September and the latter from 

 September to March. 



It happens, therefore, in dealing with large 

 areas, that during the same period of time 

 (that is generally, but not invariably, six 

 months) the pressure is above the normal 

 in some places and below the normal in 

 others. In interpreting the curves, therefore, 

 it should be borne in mind that in the one 

 case in which high-pressure months are con- 

 sidered, the crests of the curves denote times 

 of increased pressure, or an excess above the 

 normal conditions, while in the other, where 

 the low-pressure months only are employed, 

 the crests represent the times at which the 

 pressure is not so low as usual. 

 Dealing first with the region about India, the accom- 

 panying curves (Fig. 2) illustrate the variations of pres- 

 sure which have been analysed. In this set of curves, 

 about the same months are in question, so that the pressure 



to »M 



PRESSURE *'. 

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SYDNEY 



variations refer to the low-pressure (summer) months in 

 the northern hemisphere and to the high-pressure (winter) 

 months in the southern hemisphere. 



Commencing with Indian pressures (as represented by 

 Bombay), the area was gradually extended to Ceylon 



