the diurnal va- 

 riations of the 

 barometer. 



HlSrORT of the SOCIETK 23 



the difcoveries, which Dr Monro has made in the Stru6lure of 

 the Brain, the Ear, &c. could not be fufficiently underftood 

 without the numerous plates by which they are illuftrated, it 

 is unnecelTary to attempt any detail of their contents. 



Phjf. CL A paper, by Dr Balfour of Calcutta, was com- 179-6- 



municated, on the Diurnal Variations of the Barometer. Dr Klfou'l'on 



Dr Balfour's Obfervations, on the Diurnal Variations of 

 the Barometer, were made at Calcutta, and communicated to 

 the Afiatic Society in 1 794. A copy of them, which he fent to 

 a friend in Edinburgh, was the paper now read in the Royal 

 Society. 



The {ituation in which thefe obfervations were made, entitlej? 

 them to peculiar attention ; for it is well known, that, between 

 and near the tropics, the barometer is very fteady, and free from 

 thofe great and fudden changes that take place in higher lati- 

 tudes. It is in fuch fituations, therefore, that the fmaller periodi- 

 cal variations of the barometer, if they exift at all, are likely to 

 be difcovered, as being feparate from thofe accidental irregulari- 

 ties with which they mull be complicated in our northern cli- 

 mates. 



Dr Balfour's diligence, in obferving the barometer, has al- 

 fo been fingularly great. He impofed on himfelf the talk of 

 obferving the flate of that inftrument every half hour, for an 

 entire lunation, from the new moon on the 31ft of March, to 

 that of the 29th of April 1794. 



The refult was, the difcovery of a periodical variation in the 

 barometer, confifting of two ofcillations, which it performs re- 

 gularly every twenty-four hours. 



I. On every day, that Dr Balfour obferved, with fcarce 

 any exception, the barometer conftantly fell between ten at 



nighr 



