I348

The Neck of a Man, or the like Part of any other Body, rais'd perpendicularly, and covered with the Prominency of some other Part, will appear more obscure, than the Face, or Side perpendicular to the Part so Prominent. This follows from an Axiom which will be easily allowed, viz. That every Body will be the more illumined, as it receives Light from a greater share of its luminous Body. Thus, in [Tab. 2. Fig. 8.] the Point A is not illumined by any Part of the Heavens K F, the Point B is illumined by the Part K H, the Point C, by the Part or Arch G K, and the Point D is illumined by the entire Arch K F; so that the Stomach will be found equally enlighten'd with the Forehead, the Nose and the Chin; the Points C and B, at the same time, being less enlighten'd, and the Point A none at all. Now, with regard to Faces, it must be observ'd, that at different Distances, their several Shadows disappear; none being at length found remaining, but those of the Orbits of the Eyes, and of some other the like Parts; and further, that at a great Distance, the Shadows do all cease to be seen, the Lights which shou'd show them, being weaken'd, and at length, entirely lost, by Reason of their smallness, and the Disproportion they bear to the Shadows; So that the whole Face becomes obscure, and appears invested with one general half-Shadow. Not that there is any real Alteration, either in the Lights, or Shadows themselves; for the Ef fect is wholly owing to the Distance, which weakning their Force and Impression, disables them at last, from distinguishing themselves; so that mingling together, they form what we call a Half-shadow. Thus, 'tis Distance in like manuer, which makes Trees, and other Bodies, appear more Obscure, than they are in Reality: And, thus 'tis Distance, which occasions that Azure Colour, wherewith all remote Bodies appear, and which is seen the most sensibly, in the shadowed Parts; those more illumined, being more able to preserve their Native Colours, Genuine, and unadulterated by the Air.