Fourthly, it cannot arise fpom aay uncertainty in the max- 

 imum of aberration of light; whether we take the maximum 

 at 30" or 20i" Because when « Lyrae passes the meridian 

 near noon and midnightj the aberration is very small, and 

 therefore not affected by a small error in the maximum. 



But it is necessary to compute with precision according to 

 the sun's longitude at the time of the passage, as the aberra- 

 tion changes rapidly at these times. The semi annual equa- 

 tion is nearly the same at these times, and therefore no error 

 from thence. The precession or any small uncertainty in the 

 quantity of proper motion can occasion no en'or; 



When indeed « Lyrce passes near 6 o'clock, then an un- 

 certainty in the maximum of aberration may affect, the con- 

 clusion, because the aberration in declination is nearly a max- 

 imum, and therefore in this enquiry it is of some consequence 

 to know the maximum of aberration. 



Hence the observations of » Lyr^ near quadrature aie less 

 proper for this enquiry, and have accordingly been less aU 

 tended to. Those that have been made are however, very* 

 consistent with the observations made near noon and mid-' 

 night. 



The only solution, perhaps that we have left, unless we 

 admit of parallax, is, that in different degrees of tempera- 



ent laws of change of denaity frpip change of temperature in Bradley's, aad in the 

 French Tables.^ — In « Lyrae.it is scarcely wortli notice, but is considerable in » Aquilte. 

 In, that, star the parallax comes out legs by the French, than by Bradley's Refractions. 



