of the Barometric Formulm^ ^'c. 663 



POSTSCRIPT. 



(Read May 9, 1859.) 



In the foregoing paper I particularly pointed out that, notwithstanding the 

 great improvements produced by my new Formulce, having new Constants, 

 assisted by Tables of Local Horary Correction, we ought not to expect exemp- 

 tion from serious error on all future occasions. My reasons for this my belief 

 were stated at pages 638, 639, and 640. At page 639 commences the follow- 

 ing statement : — 



" Now, it is to be remarked, that according to the Table of Horary Correc- 

 tions, I had reason to expect such errors to be little removed from nothing. 

 Great, therefore, was my disappointment. Yet there is this consolation in such 

 disappointment, that had the formula of Laplace, or anj' other derived from 

 Laplace (such as Bayley's or Poisson's) been employed instead of my own 

 formula, the errors had been double of the actual errors, as given in the small 

 Table IV., so that, although the Table of Horary Corrections meet not our 

 wishes nor our expectations, it diminishes by one-half the errors of the other 

 formulae. Therefore, let us not despond ; all we desire has not been realized, 

 but considerable improvement has been made, and by diligence and zeal more 

 may hereafter be done. The defect of the formula which now remains to be 

 remedied is brought within a small compass, and is simply the error occasioned 

 by assuming an incorrect value of the mean temperature of the atmospheric 

 column between the stations of observations. Time only can tell if any consi- 

 derable improvement be possible in reference to mean-temperature errors, but 

 these, if not removable by positive improvements in the formula itself, may be 

 rendered for practical purposes comparatively innoxious, by sound tables of 

 local horary correction ; and in the formation of such tables, the new formula 

 with new constant, will give, I believe, very important assistance." 



Now, in reference to this extract, I have to remark, that in consequence of 

 information lately communicated to me by Monsieur E. Plantamode, I have 

 to modify, very considerably, my opinion concerning the mean-temperature 



vol. xxnr 4 s 



