1825. J Astronomical Society, I W 



now's arrangement of the Ferns, whereas Mr. Brown's work 

 made its appearance in the same spring, but before Willdenow's, 

 and his arrangement is materially different." ..,5 ^,,. 



A farther portion of Dr. Hamilton's Comment^ifyi,*6i^»(t]je 

 third part of the Hortua Malabaricus was also rea(}Hif(x9 .8- tM 



ASTRONOMICAL SOCIETY. / ■ 



May 13. — The reading of Mr. Henry Atkinson's elaborate 

 communication on the subject of Refraction was concluded. 

 In the course of this paper the author has collected and ar- 

 ranged a great variety of meteorological observations, made in 

 different seasons, and at different parts of the world, for the 

 purpose of enabling him to ascertain the mean temperature at 

 the equator and in different latitudes, as well as the law of 

 variation in the temperature of the air at different heights 

 above the level of the sea. From these data he has deduced 

 formulae, by the use of which the computed and observed mean 

 temperatures in any given place, or at any given height, ap- 

 pear to agree in a remarkable manner. His next inquiry is, 

 to ascertain the law by which the height and the elasticity of 

 the air is connected ; and also the relation between the elastic 

 city and density at any given height. These inquiries are 

 guided by observations and experiments that have been made 

 and pubhshed by men of eminence in this department of 

 science. The reasoning and deductions are founded on ac- 

 knowledged facts ; and hypothesis furnishes no part of the data 

 from which the tables, founded on these investigations, are 

 computed. Astronomical observations supply no portion of the 

 materials which form the basis of the computations, but all 

 the results are obtained by formulae depending on optical pin- 

 cip/es; so that the near agreement of the quantities contained 

 in these tables (when properly collected) with those given by 

 the most approved modern tables of refraction proves that the 

 various formulae by which these quantities were obtained are 

 founded in nature, as well as happily applied. The atmosphere 

 is divided into a variety of strata, and each stratum has its 

 appropriate formula for determining its share of mean refraction ; 

 and when the different portions belonging to the different strata 

 are put together in succession, they constitute such an ar 

 rangement of quantities as proceed by a regular gradation, or 

 very nearly so ; and nothing but a close examination of the 

 differences can detect that the whole succession has not de- 

 pended on one continued formula. Besides the atmospheric 

 refractions adapted as corrections for celestial observations, 

 the author has applied one of his formulae successfully to de- 

 termine the terrestrial refraction as it has reference to two 

 objects standing in different elevations : so that whether this 

 memoir be considered as a meteorological, geodetical, or astro- 



