Thus, if the sun’s altitude were 26°, the height of the primary bow would 16° 2´, and of the secondary, 28° 10´. It follows, that the height and the size of the bows diminish as the altitude of the sun increases. 7. If the sun’s altitude is more than 42 degrees, and less than 54°, the exterior bow may be seen though the interior bow is invisible. 8. Sometimes only a portion of an arch will be visible while all the other parts of the bow are invisible. This happens when the rain does not occupy a space of sufficient extent to complete the bow; and the appearance of this position, and even of the bow itself, will be various, according to the nature of the situation, and the space occupied by the rain. The appearance of the rainbow may be produced by artificial means, at any time when the sun is shining and not too highly elevated above the horizon. This is effected by means of artificial fountains or _Jet d’eaus_, which are intended to throw up streams of water to a great height. These streams, when they spread very wide, and blend together in their upper parts, form, when falling, a shower of artificial rain. If, then, when the fountain is playing, we move between it and the sun, at a proper distance from the fountain, till our shadow point directly towards it, and look at the shower,--we shall observe the colours of the rainbow, strong and vivid; and, what is particularly worthy of notice, the bow appears, notwithstanding the nearness of the shower, to be as large, and as far off, as the rainbow which we see in a natural shower of rain. The same experiment may be made by candle-light, and with any instrument that will form an artificial shower.