Light striking sharply on one side, as when a lantern picture is thrown obliquely against a wall, making the nearest edge sharp against a deep dark, and drifting into shadow by degrees, thus founding the principles of light and shadow. Light-acute, half-light, middle-tint, dark-acute, half-dark, and middle-tint. Burnet gives a great number of examples to prove the justice of his theory, which to give here would only be a loss of time, as they repeat those different orders of lighting, yet I may with benefit quote the wise advice of Rubens to his students, where he says, 'Begin by painting in your shadows lightly, taking care that no white is suffered to glide into them, for it is the poison of a picture except in the lights; if even your shadows are corrupted by the introduction of this baneful colour, your tones will no longer be warm and transparent, but heavy and leady. It is not the same in the lights, they may be loaded with colour as much as you think proper.' A sheet of white paper or a clean piece of primed canvas will give us a good idea of the value of shadow: make a stain upon any portion of its surface, say two shades deeper grey than the canvas, and you have the effect of light and half-tint. In open-air effects be sparing of your darks, so that strength and force may be the consequence. A sheet of grey tone paper is about the best medium to impress upon you the value of tone. Make a mark with white chalk and a few darks, and the ground will give all the other qualifying powers needful; the fewer markings you make the more strength you must get in your effect. In planning your picture, your first care, after the form has been seen to, is to ascertain where the lights are to come from, and upon what they are likely to fall; nature is our best guide in this, yet nature must be followed with great caution, owing, as I have said before, to the rapidity of her changes; also the superiority of light over white, and shadow under black; we see, for example, degrees of light without shadow, and degrees of shadow after the greatest depth of darkness has been attained, and these we can no more follow than we can follow the separate blade-markings on a grass-field; as in the one case so in the other, we must suit ourselves to our limited means and simplify the whole matter, gather our lights into a narrower and more concentrated focus, and depend upon the half-tints and reflections for the greater part of our picture. If we see a dozen ripples of light, be content with the capture of one light, and let the other eleven become half-lights or vanish altogether; so shall we secure force. Devote our skill to those half-tones which in reality mean the labour, pride, and test of the painter, even although it is the high lights and deep darks that finish the picture.