CX NOTES. 



farther explanation. In Gassendi's biographies, he says, " Magnam imprimU 

 rationem habuit Copernicus duarum opinionum affinium, qnarum unam Mar- 

 tiano Capellse, alteram Apollonio Pergaeo attribuit. Apollonius Solem delegit, 

 circa quern, ut centrum, non modo Mercurius et Venus, verum etiam Mars, 

 Jupiter, Saturnus suas obirent periodos, dum Sol interim, uti et Luna, circa 

 Terrain, ut circa centrum, quod foret affixarum mundique centrum, moverentur, 

 quse deinceps quoque opinio Tychonis propemodum fuit. Rationem autem 

 magnam harum opinionum Copernicus habuit, quod utraque eximie Mercurii 

 ac Veneris circuitiones repraesentaret, eximieque causam retrogradationum, 

 directionum, stationum in iis appaventium exprimeret et posterior (Pergsei) 

 quoque in tribus planetis superioribus praestaret" (Gassendi, Tychonis Brahei 

 Vita, p. 296). My friend the astronomer Galle, from whom I sought infor- 

 mation, like myself finds nothing which could justify Gassendi's decided 

 statement. He writes to me, "In the passages which you refer to in 

 Ptolemy's Almagest (in the commencement of Book XII.), and in the works 

 of Copernicus (lib. v. cap. 3, p. 141, a; cap. 35, p. 179, a and b; cap. 36, 

 p. 181, b), there is only question of explaining the retrogressions and sta 

 tionary appearances of the planets, in which ther is indeed a reference to 

 Apollonius's assumption of the revolution of the planets round the sun (and 

 Copernicus himself mentious expressly the assumption of the earth's standing 

 still) ; but it does not appear possible to determine where he obtained what 

 he supposes to have been derived from Apollonius. 1 can only therefore 

 conjecture, that some late writer gave a system attributed to Apollonius of 

 Perga which resembled that of Tycho ; although I do not find, even in 

 Copernicus, any clear exposition of such a system, or any quotations of ancient 

 passages respecting it. If the source from whence the complete Tychonic 

 view is attributed to Apollonius should be merely lib. XII. of the Almagest, 

 we may consider that Gassendi went too far in his suppositions, and that the 

 case resembled that of the phases of Mercury and Venus, which Copernicus 

 spoke of indeed (lib. i. cap. 10, p. 7, b, and 8, a), but without decidedly 

 applying them to his system. Apollonius, perhaps, in a similar manner may 

 have treated mathematically the explanation of the retrogressions of the 

 planets under the assumption of a revolution round the sun, without subjoin- 

 ing any thing decided and general as to the truth of this assumption. The 

 difference of the Apollonian system described by Gassendi from that of Tycho 

 would only be, that the latter explained the inequalities of the movements 

 as well. The remark of Robert Small, that the fundamental idea of the 

 Tychonian system was by no means a stranger to the mind of Copernicus, 



