the Heights of' Be7i^Lo7(i(ynd, Sfc. 123 



dcrahlc distance, were to be depended on equally with these 

 made in the immediate vicinity of the mountain of which the 

 height is to be determined, two observers readily agreed to make 

 corresponding observations in the vicinity of Edinburgh, at the 

 same time that Mr J. Adie and I were employed at Ben-Lo- 

 mond. 



Of these our friend Mr Thomas Henderson made regular 

 observations with the barometer, on the Calto» Hill, the cis- 

 tern of which is nine feet six inches above the floor of the ob- 

 servatory, and, from previous observations, 355 feet above the 

 mean height of the sea at Leith. 



In order to obtain the utmost accuracy, it was thought ne- 

 cessary to determine the correct barometric coefficient, according 

 to the circumstances of the case, rather than to take a mean, 

 which has been generally adopted. Ramond, on comparing a 

 great number of heights, determined barometrically with the 

 same, geometrically found the general coefficient at the level of 

 the sea to be 18,336 French metres; while M. Biot found, by 

 comparing the specific gravity of air and mercury, that it is 



18.334 metres at the parallel of 45° N. The mean of these is 



18.335 metres, equal to 60,155 feet, or 10,026 fathoms, at the 

 freezing point, or 32° of Fahrenheit's scale. It may be remark- 

 ed, however, that M. Biot supposes the mean height of the 

 lower barometer, in his TaUes- 4br Computing Barometric 

 Heights, to l)e 1200 metres, or about 4000 feet above the sea ; 

 and the higher barometer 2000 metr^, or about 6500 feet above 

 the lower, or 10,500 feet above the sea ; and these suppositions, 

 allowing for the difference of gravity, according to their heights, 

 give 18,393 metres, equal to 60,346 English feet, or 10,058 fa- 

 thoms, for the general coefficient, which he thinks sufficiently ac- 

 curate for ordinary barometric purposes. This is no doubt true, 

 and it is not likely that such operations will ever possess the 

 same extreme precision as those of astronomy ; yet it is proba- 

 ble, I think, that they may be much more accurate than at pre- 

 sent, if we consider the great superiority which the modern me- 

 thods possess over those of I)e Luc, Roy, &c. At all events, a 

 table of correct barometric coefficients is almost as easily applied 

 as the mean one in a great range, obviously in both extremes 



