244 Mr. Galbraith on the Obliquity of the Ecliptic. 



Table of the Values of the Obliquity of the Ecliptic from the 

 most remote periods for which it has been recorded ; com- 

 pared with that deduced from the annual variation now 

 obtained, and applied to the obliquity of 1820. 



No. 



1 



2 



3 



4 



5 



G 



7 



8 



9 



10 



11 



12 



13 



14 



IS 



16 



17 



18 



1!) 



20 



3] 



22 



23 



24 



85 



96 



Observers. 



Eratosthenes 



Hipparchus 



Ptolemy 



Pappus 



Albategnius 



Arzahel 



Cocheou-King 



Prophatius 



Ulug-beg 



Regiomontaniis 



Waltherus 



Copernicus 



Tycho Brahe 



Cassini (father) 



Hevelius 



Cassini (son) 



Richer (at Cayenne).. 

 Flamsteed (himself).. 

 Do. (accord 6 toLalande) 

 Lahire, in his Tables . 



Roemer 



Louville 



Condamine 



Lacaille 



Mayer 



Bradley 



Year. 



230 B.C 



140 



140A.C 



390 



880 

 1070 

 1278 

 1300 

 1437 

 1460 

 1490 

 1500 

 1587 

 1656 

 1660 

 1672 

 1672 

 1690 

 1690 



1706 

 1716 

 1736 

 1750 

 1750 

 1750 



Obs. 

 Obliquity. 



20 

 20 



23 51 

 23 51 

 23 51 10 

 23 30 

 23 35 40 

 23 34 

 23 32 12 

 23 32 

 23 30 27 

 23 30 

 23 29 47 

 23 29 24 

 23 29 30 

 23 29 2 

 23 29 30 

 23 28 54 

 23 28 52 

 23 28 56 

 23 28 48 

 23 29 

 23 28 47 

 23 28 31 

 23 28 24 

 23 28 19 

 23 28 18 

 23 28 18 



Comp. L.jr 

 Obliquity. 



23 42 

 23 42 

 23 40 

 23 38 

 23 34 

 23 33 

 23 31 

 23 31 

 23 30 

 23 30 

 23 30 

 23 30 

 23 29 

 23 28 

 23 28 

 23 28 

 23 28 

 23 28 

 23 28 

 23 28 

 23 28 

 23 28 

 23 28 

 23 28 

 23 28 

 23 28 



58 

 18 

 14 

 23 

 45 

 20 

 48 

 38 

 37 

 27 

 13 

 9 

 30 

 59-5 

 57-7 

 52-4 

 52-4 

 44-3 

 44-3 

 44-3 

 37-2 

 32-8 

 23-9 

 17-66 

 17-66 

 17-66 



- 9 

 -10 

 + 8 



- 



- 



- 



- 

 + 



+ o 







- 



- 



- 



+ o 



- 



- 



- 



- 

 

 

 

 

 



+ 



2 



56 



23 



55 



40 



24 



22 



10 



27 



26 



45 

 

 2-5 



32-3 

 2-6 

 0-4 



117 

 3-7 



15-7 

 9-8 

 1-8 

 0-1 

 1-34 

 0-34 

 0-34 



From the above table it appears that the deviation of 

 theory from observation is considerable for the observations 

 made about two centuries ago. As the instruments employed 

 in making observations by the early astronomers were very 

 rude, and could not be depended upon nearer than a fourth 

 or fifth of a degree, and as no allowance was made for refrac- 

 tion, because it was then unknown, such discrepancies may 

 naturally be expected. 



The first four observed obliquities deviate most consider- 

 ably from the computed ; but all who are aware of the state 

 of astronomy, and of the rude manner of making observations 

 with very imperfect instruments at those times, will not be sur- 

 prised at such a circumstance. From the time of Albategnius 

 to that of Tycho Brahe, the discrepancies are all much less, 

 being within a minute of each other, which is as much as can 

 be expected, since all the observations were made with in- 

 struments 



