18?3.] fo7' Barometrical Measurements » 365, 



These results compared with the former set show the degree 

 of correspondence between experiment and deduction from the 

 barometric formula. The formula of Laplace agrees most nearly 

 with experiment ; the difference admits of a satisfactory expla- 

 nation if we only consider the different quantities of moisture 

 held in solution by the air, under the very different circumstances 

 of a conftned room, and the top of a mountain ; and this differ- 

 ence being only about ^— d part would only affect the accuracy 



of about 10 metres even in the height of Chimborazo ; and after 

 all, the ratios which the formula gives, being so many means 

 deduced from a great number of observations, and so many con- 

 clusions deduced from operations on a large scale, and applied 

 to those on a small, are more proper to give confirmation to the 

 results of experiment than to receive it from them. 



In a note appended to the beginning of the second memoir, 

 M. Ramond quotes an account of a more recent determination 

 of the ratio of the weights of air and mercury ; which results 

 1 : 10463, the air being perfectly dry : in the latitude of Paris, 

 temperature 0°, pressure 0*76 m. This result was obtained by 

 MM. Arago and Biot. From it they deduce the barometric 

 coefficient, for lat. 45 in metres, 18316*6 for dry air, and 

 18351*8 for air saturated with moisture ; and for the mean state 

 18334*2, which is very nearly equal to that adopted by M. Ra- 

 mond from observation confirmed by geometrical measurement, 

 viz. 18336. 



III. Under the head of "Isolated Observations," M. Ramond 

 discusses the question of the decrease of temperature as we 

 ascend in the atmosphere. He has given in the original, a table 

 exhibiting this decrease from a variety of observations, the result 

 of which examination only I have preserved in the foregoing 

 abstract. The reader will find the supposition of an uniform 

 decrease (which M. Ramond took as a mean value convenient 

 for practical purposes), confirmed by reasoning a priori in the 

 valuable paper on Barometrical Measurements, by Prof. Play- 

 fair, in the Edinb. Transactions, vol. i. 1788, and since repub- 

 lished in his works, vol. iii. 1822. In this memoir. Part III. the 

 author investigates the law of decrease in the heat of the differ- 

 ent strata of air as we ascend. He gives a demonstration, 

 proving, that abstracting from certain anomalies annual and 

 diurnal, as well as from accidental irregularities, the decrease is 

 uniform. This proof is deduced upon the principle, that the 

 sun's rays do not heat the air in their passage through it; a fact 

 established by many concurrent experiments. 



W, In adverting to the necessity of reducing the mercuiy in 

 the cistern of the barometer to a constant level, M. Ramond has 

 mentioned several contrivances of distinguished foreign artists 

 for this purpose. The accuracy, however, of all such expedients 

 appears very questionable ; and as a constant point of depar^u^^- 



