52 ESSAYS AND OBSERVATIONS 



its red extremity neareft to its true place. Irx 

 tb ftars fituated near the pole of the ecli-!- 

 ptic, its length fliould continue always thd 

 fame, tho' directed along all the different 

 fecondar es of the eclip.ic in the courfe of 

 a year : but, in thoie which lye in or near 

 the plane of the ecliptic, it fhould be 

 greateil: . at the limits of the eaftern and 

 weftern aberrations ; the ftar recovering its 

 colour and figu'e when the true and mean 

 places coincide. But, there is no hope of 

 diTcovering, whether our hypothecs be true 

 or falfe, by this cpnfequence of it j for the 

 greatefl length of the dilated difk, being, to 

 the whole aberration, as the difference of 

 the velocity of red and violet to the mean 

 velocity of light, i, e. as i to 'jj nearly, 

 (N"' 39.) cannot much exceed one fourth 

 part of a fecond j for the greateft aberration 

 is but about twenty feccnds. 



49. The time which the extreme violet 

 takes to move thro' any fpace muft be, to 

 that which the red takes, as 78 to JJ. If 

 yupiter be fuppofed in a quadrate afpe(ft with 

 the fun, in which cafe the eclipfes of hi^ 

 fatellites are moft commodioully obferved, 

 |iis diftance from the earth being nearly equal 



