I remember witnessing an especially brilliant sunset last autumn on the high-road between Kirriemuir and Blairgowrie. The setting sun shone upon the back of certain long trailing clouds which were much nearer me than a range behind. The fringes of the front range were brilliantly golden, while the face of those behind was sparklingly bright. Then the sun disappeared over the western hills, and his place was full of spokes of living light. Looking eastward, I observed on the horizon the base of the northern line of a beautiful rainbow--"the shepherd's delight" for fine weather. Soon in the west the light faded; but there came out of the east a lovely flush, and the general sky was presently flamboyant with afterglow. The front set of clouds was darker except on the edges, the red being on the clouds behind; and the horizon in the east was particularly rich with dark red hues. Gradually the eastern glow rose and reddened all the clouds, but the front clouds were still grey. The effect was very fine in contrast. The fleecy clouds overhead became transparently light red, as they stretched over to reach the silver-streaked west. The new moon was just appearing upright against a slightly less bright opening in the sky, betokening the firm hardness of autumn. Soon the colouring melted away, and the peaceful reign of the later twilight possessed the land. Now why that brilliancy of the east, when the west was colourless? Most of all you note the immense variety and wealth of reds. These are due to dust in the atmosphere. We are the more convinced of this by the very remarkable and beautiful sunsets which occurred after the tremendous eruption at Krakatoa, in the Straits of Sunda, thirty years ago. There was then ejected an enormous quantity of fine dust, which spread over the whole world's atmosphere. So long as that vast amount of dust remained in the air did the sunsets and afterglows display an exceptional wealth of colouring. All observers were struck with the vividly brilliant red colours in all shades and tints. The minute particles of dust in the atmosphere arrest the sun's rays and scatter them in all directions; they are so small, however, that they cannot reflect and scatter all; their power is limited to the scattering of the rays at the blue end of the spectrum, while the red rays pass on unarrested. The display of the colours of the blue end are found in numberless shades, from the full deep blue in the zenith to the greenish-blue near the horizon.