344 On Pefraction. 



than 45° of altitude : and he is generally considered as 

 the first who proved that it reached all the way to the 

 zenith*. He also supposed that near the equator the 

 horizontal retraction was less than in our climate by 

 about one-third ; that this difference decreased as far up 

 as 60°, after which it was the same nearly for both cli- 

 mates. 



From this discovery it followed, as a natural conse- 

 quence, that the refraction must be greater near the pole 

 than at Paris : and this was shortly afterwards proved to 

 the Academy by the publication of a work expressly on 

 that subject f. The king of Sweden, being in 1694 at 

 Tornea in West Bothnia, near the latitude of 65° 45', and 

 observing that the sun did not set there in the summer sol- 

 stice, sent the following year some mathematicians to 

 make more certain and exact observations of this curious 

 phenomenon. They are contained in this book, and 

 Messrs. Cassini and De la Hire J concluded from them, 

 that in the latitude of 65° 45' the horizontal refraction must 

 be 58', or nearly double of that at Paris. 



According to an observation made by some Dutchmen§ 

 who passed the winter of 1596-7 in Nova Zembla, in lati- 

 tude 76° north, the sun, which had entirely disappeared the 

 14th of November, began to rise again the 24th of January, 

 viz. six days sooner than was expected according to astro- 

 nomical calculations ||. If so, when the sun has been two 

 or three months under the horizon, as the Dutchmen ob- 

 served in 1597, the cold becomes dreadful, and perhaps 

 the refraction increases prodigiously. M. le Monnier as- 

 sures us, that he found by the observations printed in 1599, 

 that the 24th and 27th of January 1597, there were more 

 than 4\ degrees of refraction : that he could neither explain 

 these observations, reject them as doubtful, nor suppose 

 any error, as was done bv most of the other astronomers, 

 Kepler, Cassini, Scotto, and, lastly, M. le Gentilf, who 

 maintained that there were errors in the observations, and 

 accordingly read a memoir on the subject. If it were not 

 so difficult a task to winter in these high latitudes, we 

 might expect such observations as would remove all doubt 



* Mem. de l'Acad. 1700, p. 1 12. 



f " Refractio solis inoccidui," &c. Holmiae, 4to, 1 695. These observations 

 in Lapland were made by Messrs. Spole and Bilberg. 



\ In two papers of remarks on these observations published by them in 

 the Mem.de I'Acad. 1700, p. 37. 



§ Smith's Optics, p. 61. Remarks. Dr. Jurin's Notes on Varenius's 

 Geography, vol. i. p. 441. || Leipsic Acts, 1G79. 



\ Voy. dans les Mers des Indes, torn. i. p. 395; torn. ii. p. 832. 



on 



