of the Barometer near Edinburgh. 165 



The monthly oscillations at the remarkable station of the Grand 

 St Bernard will be noticed in Section 1 1 . 



8. Without dwelling farther at present upon the deductions 

 from my own observations, I proceed to make some inquiry into 

 the law which regulates the geographical distribution of this re- 

 markable phenomenon. 



The general fact that the amount of the barometric oscilla- 

 tion decreases from the Equator towards the Poles, has been 

 long established. The active researches of HUMBOLDT, between 

 the tropics, above thirty years ago, excited a spirit of inquiry in 

 Europe, in which the distinguished RAMOND took the lead, and 

 which terminated in the detection of the horary oscillation among 

 the great accidental variations of atmospherical pressure, at the 

 same hours nearly, but much smaller in amount, than in lower 

 latitudes. The labour of observation was therefore greatly in- 

 creased, requiring some years of accurate data to afford the desir- 

 able precision as to amount, which might be obtained by a few 

 days observation near the Equator. Allowing for accidental ir- 

 regularities, the progressive decrease has been very satisfactorily 

 proved; but two very remarkable registers have, within the 

 last few years, furnished us with unexpected and curious results, 

 which must occupy a prominent place in any theory on the sub- 

 ject. The first of these was the register kept at the convent of 

 the Grand St Bernard, which, as well as a precisely correspond- 

 ing one at Geneva, was adapted to the investigation of the horary 

 oscillations, immediately after the publication of the third vo- 

 lume of HUMBOLDT'S " Relation Historique." The St Bernard 

 observations demonstrate, by the regular annual results of the 

 last five years (1826-30), that, at 8000 feet above the sea, the 

 barometer is lowest at 9 A. M. and highest at 3 P. M., precisely the 

 reverse of what had hitherto been observed. HUMBOLDT had 

 remarked that, between the tropics, though the amount was di- 

 minished, the hour of maximum was not changed. These two 



VOL. XII. PART I. Y 



