the Barometric Formulce, S(C. 637 



rect. This peculiarity of my own formula is but of little value if it give more 

 trouble in actual calculations ; but as my formula is more simple in its v^orking, 

 its mathematical correctness is an additional recommendation of it. 



I have to observe that the expression %y{ff'), which may be designated 

 the hygrometric element, and which 1 have expressed, for sake of simplicity, by 

 the character £ in the formulse which I have given in the last pages of this 

 paper, differs (but insensibly) from the corresponding hygrometric element 



of Bessel's formula, which is „„ ,„„ <^Fi- Ii the last pages of this paper I 



o74U7 



employ the character 8' (delta aspirated), for sake of simplicity, to designate the 



25610 

 quantity aFi ; and in the Appendix I prove that for practical purposes 



8 = 8', and that the one may, therefore, be employed indifferently for the other. 



I have also given in the Appendix Bessel's equation for calculating the 

 elastic forces of vapour of water for the temperatures corresponding to such 

 forces, and I have found such equation of Bessel to give results very nearly 

 the same as those I have obtained from the Tables of Dr. Anderson, calculated 

 from experiments of Dalton and TJee ; the agreement is shown in the 

 Appendix. 



As the purport of this paper is not to explain the peculiarities of Bessel's 

 formula, I have to state that any one anxious to see it in full may do so by 

 consulting M. Plantamoue's quarto, "Kesume," at pp. 63, 64, 65, 66, and 

 67. M. Plantamour found it so obscure and different from other formulas in 

 general use, that he has devoted several pages in transforming it, and I frankly 

 confess that, even thus transformed, it appears to me still very complicated. I 

 have also taken the troiible to give it a form which may be found in the last 

 pages of this Paper, and such form, I hope, will appear to the Academy suffi- 

 ciently simple for the actual work of calculation. Nevertheless, though thus 

 simplified, I can confidently pronounce it inferior, as to facility of calculation, 

 to my own, which requires only, in addition to the labour of the old formulas, 

 the simple subtraction of the hygrometric element, 8= %y(/f) from the cor- 

 rected barometric pressures. 



Having now enlarged on the importance, and, I ought to say, the indispen- 

 sable necessity of a sound Table of local horary corrections, in order to secure the 



