Geographical Distribution of Plants in YorJcshiie. 211 



Visible altitude of the sun's lower limb =31° 7' 34/'-7 

 Sun's semidiameter ... ... = 1551*8 



Sun's parallax in altitude ... = 7 '2 



31 23 33 -7 

 Ref. corrected for bar r , ther r , &c. =— 1 31 '7 



31 22 2 



True altitude of the sun's centre = 58 37 58 



* As 360° : 51° 33' W'6 : : 24 h — 16 s *3 : 3" 26 m 12 s -6 

 Eq. of time at the instant of observation = 1 47'9 



Mean time = 3 28 0-5 



Secondly. For the reduced latitude, the mean time by the 

 above method of calculation is found equal to 3 h 28 m 34 i *4-. 

 So that it appears even in this instance there is a difference of 

 33''9, and in some cases it would be much greater ; this is of 

 material consequence where great accuracy is required, and 

 therefore I must repeat that I should be much obliged to any 

 of your scientific correspondents to inform me which latitude 

 I must invariably use, and whether the process in the above 

 solution is in every other respect perfectly correct for obtain- 

 ing the requisite accuracy so much desired. 



I remain, Gentlemen, with great respect, 

 Your obedient servant, 

 Pertenhall, Kimbolton, SAMUEL COOPER. 



Sept. 1, 1824. 



P.S. Is the sun's right ascension as given in the Nautical 

 Almanac, expressed in solar or sidereal time ? 



In using Dr. Tiarks's tables for finding mean solar time 

 (given at pages 280 and 281 of vol. 62 of your Journal), should 

 not the variation of the equation of time, in the interval of the 

 sun's passing the meridian, and that of the star, be applied to 

 the computation, when we wish to obtain the exact mean solar 

 time? 



XXXVIII. Sketch of the Geographical Distribution of Plants 

 in Yorkshire. By J. Atkinson, Esq. F.L.S. fyc. Leedsf. 



T^IIE county of York, situate in parallel 53° and 5*° N., is 

 ■*■ not less distinguished for its size than for its varied sur- 



* I conceive this proportion necessary, because the solar days are not all 

 accurately equal to 24 hours, but to 24" + the variation of the equation of 

 time for that day. 



f From the Memoirs of the Wernerian Society, p. 277, vol. v. part I. 

 D d 2 face? 



