the Barometric Formulce, Sfc. 635 



Having thus proved by well-ascertained facts the serious errors to whicli 

 barometric calculations are subject, even in employing the most approved for- 

 mula3, I have to remark that Tables of horary corrections, in the nature of 

 things, have only a local application. Were proof of this required, we have it 

 in the tract, "Surle Nivellement du Grand-Saint-Bernard," at pages Hand 12. 

 M. Plantamour states that, having applied his small Table of horary 

 corrections to two sets of barometric and hygrometric observations made by 

 himself, in the valley which connects Martigny with the Convent of Saint 

 Bernard, the use of his Table did good service as to one set of observations, 

 but when applied to the other, actually introduced error equal in quantity to 

 that of the horary correction. 



It follows from this fact, that the large Table prepared by me is only good 

 for the stations which have furnished the observations from which it has been 

 calculated, namely, the Convent of the Great Saint Bernard and the Obser- 

 vatory of Geneva. En attendant, a sound local Table for the locality of Dublin 

 and for other districts, I see nothing better to be done than to employ Baylet's 

 formula for observations made near to noon of the summer months ; and for 

 other periods of the year to employ my own formula, or that of Bessel, with 

 the best Table of horary corrections which can be had ; and when no table of 

 corrections, trustworthy, is forthcoming, then to be careful to work with 

 observations made near to sunset, or to two hours after sunrise. For, in employ- 

 ing Batley's formula at such times, it virtually contains the horary correction. 

 As to observations made near to sunset, or two hours after sunrise, my own 

 formula contains implicitly the horary corrections, which vanish at such 

 moments. I am now desirous to state to the Academy, in words as few as 

 possible, the peculiar difference in form of the formula of Bessel, and of my 

 own, already published by the Academy. 



Every one acquainted with barometric formulas knows that such formula 



maybe represented by H—Nx log ^,. I now speak of formulae which make no 



correct allowance for the hygrometric state of the atmosphere, and, therefore, I 

 make exception of the formula of Bessel and of my own. 



In this equation, viz., H=Nx log -77,, H indicates the height of one station 



