faded red which spread above it, the sun-forsaken mountains laid their cold and ghostly heads. The ruddy colour vanished more and more; the stars strengthened in lustre, until finally the moon and they held undisputed possession of the blue-grey sky."[11] [11] Mountaineering in 1861 (Longman). Marvellous sunsets are to be witnessed from the mountains of the New World. The following is a short and graphic description of sunset glories on the Sierra Nevada Mountains by Mr. Clarence King, whose name is well known to geologists:-- "While I looked, the sun descended, shadows climbed the Sierras, casting a gloom over foothill and pine, until at last only the snow summits, reflecting the evening light, glowed like red lamps along the mountain-wall for hundreds of miles. The rest of the Sierra became invisible. The snow burned for a moment in the violet sky, and at last went out." These marvellous effects appeal powerfully to our sense of beauty and produce in most minds feelings of intense delight; but they also appeal to the reasoning faculty in man, and an intelligent observer naturally inquires, "Why are these things so? How are those glorious colours of crimson, orange, and yellow produced?" A full explanation cannot be attempted here; but this much may perhaps be said without tiring the patience of the reader. White light, such as sunlight or the light from an electric arc, is composed of all the colours of the rainbow,--violet, indigo, blue, green, yellow, orange, and red. A ray of sunlight on passing through a prism is split up into all these colours in the above order, and we get them arranged in a band which is known as the spectrum. Thus it is proved that white light is made up of all colours (black is not a colour, but the absence of colour). Now, when the sun is low down in the sky, as at sunset, only some of these colour-rays are able to pass through the atmosphere and so to reach our eyes, while others are stopped in passing through very many miles of atmosphere (as they must obviously do when the sun is low). Those which are stopped are the blue rays and others allied to blue, such as purple and green; but the red and yellow rays are able to pass on till they come to us. Hence red, yellow, and orange are the prevailing sunset tints.