A rainbow in nature has a life of appreciable duration, and so may be appropriately used in landscape, but obviously it should be regarded as a minor accessory except where it forms a necessary feature in the design.[a] The great drawback in a prominent rainbow is that it forces itself upon the attention of the observer to the detriment of the picture as a whole, and if it be very conspicuous and crosses the middle of the painted view, as in Turner's Arundel Castle, the picture appears divided in two parts, and the possibility of an illusion of opening distance is destroyed.[b] Almost as bad is the effect when a rainbow cuts off a corner of a picture, for this suggests at first sight an accidental interference with the work.[c] Of all artists Rubens seemed to know best how to use a rainbow. He adopts three methods. The first and best is to put the bow entirely in the sky[d]; the second to throw it right into the background where part of it is dissolved in the view[e]; and the third to indicate the bow in one part of the picture, and overshadow it with a strong sunlight thrown in from another part.[f] Any of these forms seems to answer well, but they practically exhaust the possibilities in general design. A section of a rainbow may be shown with one end of it on the ground, because this is observable in nature[g]; but to cut off the top of the arch as if there were no room for it on the canvas is obviously bad, for the two segments left appear quite unnatural.[h] [a] As in Martin's I have Set My Bow in the Clouds. [b] In the Rivers of England series. [c] The Rainbow of Millet, and a similar work of Thoma. [d] Harvest Landscape, Munich Gallery. [e] Harvest Landscape, Wallace Collection, London. [f] Landscape with a Rainbow, Hermitage, Petrograd. [g] Rubens's Shipwreck of Æneas, Berlin Gallery. [h] A. P. Van de Venne's Soul Fishery, Amsterdam. The small rainbows sometimes seen at waterfalls are occasionally introduced into paintings, but rarely with success because they tend to interfere with the general view of the scene. Such views are necessarily near ground, and so a bow must seriously injure the picture unless it be placed at the side, as in Innes's fine work of Niagara Falls (the example of 1884). The use of a rainbow as a track in classical pictures is sometimes effective, though the landscape is largely sacrificed owing to the compulsory great width and bright appearance of the bow, which must indeed practically absorb the attention of the observer. The best known picture of this kind is Schwind's Rainbow, which shows the beautiful form of Iris wrapped in the sheen of the bow, and descending with great speed, the idea being apparently taken from Virgil.[a] To use the top of the rainbow for a walking track is bad, as the mind instinctively repels the invention as opposed to reason.[b] [a] Æneid V., where Juno sends Iris to the Trojan fleet. [b] Thoma's Progress of the gods to Walhalla.