1876.] 



Variatiojis of the Barometer in India. 



39 



rule of similar movements at all the stations occurred on the 14th and 

 15th of February. From 10 a.m. of the 14th to 10 p.m. of the 15th, the 

 mercury fell nearly 0*3 (three tenths) of an inch at Simla ; no other fall 

 of nearly equal amount occurred within the same space of time during 

 the three months under consideration ; yet this, the largest of all the 

 atmospheric disturbances, was apparently unfelt at Madras and Singa- 

 pore. On examining the weather registers at the three stations, it was 

 found that there was a great thunderstorm at Simla, which began on the 

 horizon on the 14th of February and continued throughout the 15th. 

 There was nothiug unusual at the other stations. 



As the daily mean height of the barometer was less on Monday at 

 noon than on Saturday at noon at Simla, the fall of the mercury pro- 

 bably continued during Sunday the 16th. This great atmospheric dis- 

 turbance lasting daring three days was not propagated even to Madras, 

 the nearest station ; while the smallest of the other movements, some less 

 than 0*01 (one hundredth) of an inch, M'ere felt nearly equally well, and 

 nearly simultaneously, at all the three stations. 



"We see here a distinction between local causes of atmospheric dis- 

 turbance and that other cause which produces so many nearly simulta- 

 neous movements ; it is also easily understood that the larger deviations, 

 of 16 or 24 hours, from absolute simultaneity may be due to similar 

 though much smaller superposed local disturbances, a fact which an ex- 

 amination of the weather registers confirms. 



On the other hand, the great continuous fall of the barometer at all 

 the three stations, from the 19th to the 24th March, does not appear to 

 have been accompanied by any other unusaal atmospheric change at anv 

 one of the three stations. 



V. ^^Supplementary Note on Simultaneous Barometric \'ariations.'^ 

 By J. A. Broun, F.R.S. Received June 20, 1876. 



[Plate 1.] 



It has been pointed out in the preceding note that as we leave the 

 tropics and approach the higher latitudes we find greater apparent irre- 

 gularity in the variations of the barometric height from day to day ; 

 these irregularities are due, I believe, to different causes — one being 

 a change in the amount, and even in the direction, of the action of 

 the cause which produces so frequently within the tropics similar and 

 simultaneous movements. This change depends probably on local con- 

 ditions which affect the medium through which the actions are produced. 

 Other causes are to be found which produce variations in the mass of 

 air above the barometer. It is not to be expected, then, that the agree- 

 ment shown generally lq the barometric movements at the Indian stations 

 would appear were the investigation extended to higher latitudes ; at the 



