Mr. Ivory on the Theory of the Astronomical Refractions. 1 07 



The same rate has the authority of Professor Leslie, to whom 

 meteorology is so much indebted. If we make ^ = 4-5 fa- 

 thoms, T—T-z:: 1°, ^ ~ 480 ' ^^ ^^^^^ obtain 



/ - 9-05 -^'J - 4. ' 

 which are the numbers assumed in the paper of 1823. 



According to Dr. Dalton, another eminent philosopher 

 who has studied meteorology very successfully, and made 

 many experiments with great care, the average ascent for de- 

 pressing Fahrenheit's thermometer 1° is 300 feet, or 50 fa- 

 thoms ; this gives 



Ramond, in his Treatise on the Barometrical Formula, has 

 recorded the heights for depressing the centigrade thermome- 

 ter 1°, in 42 different experiments. Setting aside four of this 

 great number on account of their excessive irregularity, he 

 states the mean of the remaining 38 at 16<t™'7. A good 

 average may be expected from so many experiments, made 

 by observers of the greatest eminence, in different quarters of 

 the world, in every variety of height and temperature. Now 



4347-8 fathoms = 7951'"; /3 = g^; z = 164-7; conse- 

 quently 



1-/ 800x164-7 

 f " 7951x3 

 It would be a great omission in this research to leave out the 

 celebrated ascent of Gay-Lussac in a balloon. According to 

 Laplace, the whole height ascended, or 2;, is 69S0™, the de- 

 pression of the thermometer, or t'— r, being 40°-25 centi- 

 grade: hence 



1 4 / _ 800 6980 _ 



/ ~ 7951 x3 ^ 40-25 ~ 



It is to be observed that, although experience and theory 

 both concur in proving that ^ and t'— t increase together in 

 the same proportion to considerable elevations in the atmo- 

 sphere, yet, at very great elevations, there is no doubt that 

 is increases in a greater ratio than t'— t : so that when very 



great heights are used for computing — -J-^ the resulting 



value will be greater than the true quantity. What is said 



