Chap. 4. PHILOSOPHY. 239

by the prifm in that noted experiment, which will have agreat fhare in the third book of this difcourfe a . But this'opinion is at once overturned from this confideration on-ly, that the planets could be no more free from this re-fraction than the comets ; nay ought to have larger orbrighter tails, than they, becaufe the light of the planets isftrongeft. However our author has thought proper to addfome farther objections againft this opinion: for inflance,'that thefe tails are not variegated with colours, as is the"image produced by the prifm, and which is infeparablefrom that unequal refraction, which produces that diipro-portioned length of the image. And befides, when the’light in its paffage from different comets to the earth de--fcribes the fame path through the heavens, the refraction’of it fliould of neceflity be in all refpects the fame. But’this is contrary to obfervation ; for the comet in 1680,the 28th day of December, and a former comet in the*year iy77, the 19th day of December, appear’d in the*fame place of the heavens, that is, were feen adjacent to *the fame fixed ftars, the earth likewife being in the fameplace at both times; yet the tail of the latter comet de-viated from the oppofition to the fun a little to the north-ward, and the tail of the former comet declined from the •oppofition of the fun five times as much fbuthward b .

14. There are fome other falfe opinions, though lefs>regarded than thefe, which have been advanced upon this .

* Ibid. andCartef. Princ.Phil. part, 3 . § I34«& c > b Vld. Phil.Nat. princ. Math.p.i.

argument;:.