That which I have written of it is grounded especially upon that w^{ch} about 16 yeares since I affirmed to your Lo^{PP} at Welbeck, that light is a fancy in the minde, caused by motion in the braine, which motion againe is caused by the motion of y^e parts of such bodies as we call _lucid_: such as are the sunne and y^e fixed stars, and such as here on earth is fire. By putting you in mind hereof, I doe indeed call you to witnesse of it: because, the same doctrine having since been published by another, I might bee challenged for building on another man’s ground. Yett philosophical ground I take to be of such a nature, that any man may build upon it that will, especially if the owner himselfe will nott. But upon this ground, with the helpe of some other speculations drawne from the nature of motion and action, I have, I thinke, derived y^e reason of all the phænomena I have mett with concerning light and vision, both solidly enough nott to be confuted, and withall easilie enough to be understood by such as can give that attention thereto which the figures, whereby such motion as causeth vision is described, do require. All that I shall bee ever able to adde to it, is polishing: for, being the first draught, it could nott bee so perfect as I hope hereafter to make it in Latin. Butt as it is, it will sufficiently give your Lo^{PP} satisfaction in those _quæres_ you were pleased to make concerning this subject. I am content that it passe, in respect of some drosse that yett cleaves to it, for ore: w^{ch} is much better than old ends raked out of the kennell of sophisters’ bookes. And for such I commend it to your Lo^p, and myselfe to your accustomed good opinion: which hath beene hitherto so greate honour to mee, as I am nott known to the world by any thing so much as by being, My most noble lord, Your Lo^{p’s} most humble and most obliged servant THO. HOBBES. The treatise ends with the following passage:-- To conclude, I shall doe like those that build a new house where an old one stood before, that is to say, carry away the rubbish. And first, away goes the old opinion that the _shewes_ (which they call visible species) of all objects, are in all places, and all the babble _de extramittendo et intromittendo_. For their species are nothing else but fancie, made by the light proceeding directly or by repurcussion or refraction made from the object to y^e eye, and so moving the braine and other parts within. Secondly, the opinion which Vitellio takes for an axiome and foundation of his _Catoptricques_, that y^e place of y^e image by reflexion is in the perpendicular drawn from the object to the glasse. For it is false both in plaine glasses and in sphæricall, whether convexe or concave.