642 



Lieutenant Rennt on the Constants of 



Table VIII. 



Showing the Increase of Jliight due to (he Influence of the Vapour of Water of the Atmosphere, such 

 Increase heiv.g the Difference of Calculations made upon Supposition of the Atmosphere consisting of 

 simple Dry Air, and of the Atmosphere being (as it is) impregnated with Vapour of Water. 



I have in the first place to remark, that according to Table VII., the error 

 of height, A, is 5 5 feet by one observation, and only 0-2 feet by the second 

 observation for same height. As the true height of .1 is only 136-0 feet, the 

 error of the first observation cannot possibly be attributed to the incorrectness 

 of the horary correction ; therefore, it must be considered error of observation ; 

 and in reference to the heights B, C, and D of the same Table, the errors are 

 nearly the same as the error of J. ; therefore, the errors of I>, C, D are not 

 beyond the possible errors of observation. But forasmuch as every calculated 

 height near to Montreux is greater than the true heights by spirit-levelling, I 

 am persuaded that tlie corrections applied to such calculated heights are too 

 small, and this was to be expected from the locality of Montreux, a village 

 renowned for the mildness and warmth of its climate. 



I have in the second place to remark, that the errors connected with the 

 formulaj of Laplace and of Bayley, as shown in Table VIL, are obviously 

 greater tlian the unavoidable errors of observation. 



I have next to request the particular attention of the Academy to a pro- 

 posal, on my part, of a formula having a peculiar constant, whicli shall dispense 

 with hygrometric observations and hygrometric calculations on ordinary occa- 

 sions ; and yet shall make provision sufficiently correct for the liygrometric 

 state of the atmosphere. 



Before I do so, I have to correct a mistake made by me in my former paper. 



