JOURNAL 



ASIATIC SOCIETY. 



Mr. Ivory's Tables of mean Astronomical refractions, revised and 

 augmented by Major J. T. Boileau B. E. Superintending Mag. 

 netic Observatory Simla. 



The first of these Tables was published in the Philosophical Tran- 

 sactions of the Royal Society for 1823, pp. 491, et seq: and a second 

 paper and Table by the same author, appeared in the Philosophical 

 Transactions for 1838. The mean refractions for Zenith distances 

 under 8.3° correspond exactly in both the above Tables, but the re- 

 fractions differ for Zenith distances between 83° and the horizon. 



In Table I. of the original (of 1838) the mean refractions are given 

 for each degree only as far as Z. D. 70° inclusive, and thence for 

 every 10' to the horizon. In the accompanying Tables intermediate 

 numbers have been obtained by interpolation to differences of the 

 third and second order, and they have been so arranged that the 

 tabular refractions for that part of the Table of most practical utility 

 shall vary only between one and two seconds. 



The numbers in the original Table for the last degree of Zenith 

 distance, however, were found to give such irregular differences that 

 the whole of the intermediate numbers between the limits of 89° and 

 90° have been obtained by differences to the third order, from the 

 mean refraction for 89° i. e. 24' 26."8, and the horizontal refraction 

 34' 32." And although the alterations which this arrangement has 



No. 157, No. 73, New Series. b 



