626 Lieutenant Eennt on the Constants of 



could not be applied in practice; and it is in this point of view that the correct 

 formula, already communicated by me to the Academy, is possessed of greatest 

 interest. 



Although the labour undertaken by me, in co-operation with M. A. Morlott, 

 near Montreux, was in no way necessary for obtaining the new constant, yet I 

 do not regret the employment of time on such labour, forasmuch as the obser- 

 vations made at Montreux have been very useful in another direction, which 

 will appear to the Academy before this paper is concluded. 



In the midst of my work near Montreux, and after I had made use of the 

 constant 18404'9 metres (obtained from the consideration of the ratio of the 

 specific gravity of dry air to that of quicksilver), in calculating several obser- 

 vations made at that place, M. E. Plantamour, Professor of Astronomy at the 

 Academy of Geneva, having been apprised by M. Morlott of my efforts to im- 

 prove the barometric formula, forwarded to me a copy of his quarto, entitled 

 " Eesume des Observations Thermometriques et Barometriques, faites a I'Ob- 

 servatoire de Geneve et au Grand -Saint-Bernard, pendant les dix annees, 

 1841 h. 1850, suivi de tables Hygrometriques, calculees d'apres la formule de 

 Bessel, par E. Plantamouk, Professeur d'Astronomie de Geneve." M. Plan- 

 tamour afterwards sent me a second copy for the Royal Irish Academy, which, 

 with two other tracts, containing very valuable matter, I have deposited in the 

 Library of the Academy. 



The importance of these three tracts in reference to the new constant and 

 the new formula3, which make correct allowance for the hygrometric state of 

 the atmosphere, can be understood only by such persons as may have time and 

 opportunity to peruse them. 



I have now to inform the Academy that the constant which I had obtained 

 from the equation 



n 076 



making use of the experiments of Eegnault at Paris, differs from the constant 

 obtained by M. E. Plantamour from the same equation by only _the tenth 

 part of a metre (not more than four English inches) : the constant of M. Plan- 

 tamour being 18404'8 metres, my own being 18404'9 metres. The latter 

 value, viz., 18404'9 metres, had been employed by me in calculations from 



