“Distantiam præterea discimus, per mutuam quandam conspirationem oculorum. Ut enim cæcus noster duo bacilla tenens, _A E_ et _C E_, de quorum longitudine incertus, solumque intervallum manuum _A_ et _C_, cum magnitudine angulorum _A C E_, et _C A E_ exploratum habens, inde, ut ex Geometria quadam omnibus innata, scire potest ubi sit punctum _E_. Sic quum nostri oculi _R S T_ et _r s t_ ambo, vertuntur ad _X_, magnitudo lineæ _S s_, et angulorum _X S s_ et _X s S_, certos nos reddunt ubi sit punctum _X_. Et idem opera alterutrius possumus indagare, loco illum movendo, ut si versus _X_ illum semper dirigentes, prime sistamus in puncto _S_, et statim post in puncto _s_, hoc sufficiet ut magnitudo lineæ _S s_, et duorum angulorum _X S s_ et _X s S_ nostræ imaginationi simul occurrant, et distantiam puncti _X_ nos edoceant: idque per actionem mentis, quæ licet simplex judicium esse videatur, ratiocinationem tamen quandam involutam habet, similem illi, qua Geometræ per duas stationes diversas, loca inaccessa dimetiuntur.” [Illustration] I might amass together citations from several authors to the same purpose, but, this being so clear in the point, and from an author of so great note, I shall not trouble the reader with any more. What I have said on this head was not for the sake of rinding fault with other men; but, because I judged it necessary to demonstrate in the first place that we neither see distance _immediately_, nor yet perceive it by the mediation of anything that hath (as lines and angles) a _necessary_ connexion with it. For on the demonstration of this point the whole theory depends(461). _Secondly_, it is objected, that the explication I give of the appearance of the horizontal moon (which may also be applied to the sun) is the same that Gassendus had given before. I answer, there is indeed mention made of the grossness of the atmosphere in both; but then the methods wherein it is applied to solve the phenomenon are widely different, as will be evident to whoever shall compare what I have said on this subject with the following words of Gassendus:—