332 OF THE MOTION, REFRACTION,

And the same thing will follow, if, instead ofsupposing A C to be such a small tube, we ima-gine it to be the axis of a larger one ; for, fromwhat has been said, it is evident, that a particleof light at C cannot pass along that axis, un-less it be inclined to B A, in the angle BAC.

Although, therefore, the true or real place ofan object be perpendicular to the line in whichthe eye is moving, yet the visible place must bealways in the direction of the tube throughwhich the object is seen ; and the difference be-tween the true and apparent place will be greateror less, according to the proportion between thevelocity of light and that of the eye. If theearth revolves round the fun annually, and thevelocity of light, be to the velocity of theearth’s motion in its orbit, as one thousand toone, it may be proved, by a trigonometricalprocess, that the apparent place of the object,from which the light proceeds, will constantlydiffer from the true place by about three mi-nutes and an half; so that a star, placed in thepole of the ecliptic, would seem to describe acircle round that pole, the diameter of whichwould be seven minutes.

From a number of observations, made by Dr,Bradley upon the same stars for three years, hefound, that their apparent places differed fromtheir true places by about twenty seconds; andby this means it is proved, that the velocity of

light