The connection in this case is natural. Let us suppose a case in which it shall be arbitrary, or artificial. Suppose I happen to hold a rose in my hand, at the same moment a certain unusual noise is heard in the street, or at the moment when an eclipse of the sun becomes visible; on seeing the rose the next day I am instantly reminded of the noise, or of the eclipse, that was connected with it in my previous perception. _Application to the Law of Opposites._--On the same principle opposites also suggest each other. They sustain a certain relation to each other in our thoughts, and are in a sense necessary to each other in thought, as, _e. g._, white and black, crooked and straight, tall and short; which are _relative_ ideas, neither of which is complete by itself without the other; the one the complement of the other; each, so to speak, the extreme term of a comparison. As such they stand together before the mind, in its ordinary perceptions, and hence the one almost of necessity recalls the other. _The same Principle suggested by Dr. Brown._--The possibility of reducing the laws of association to one common principle, as now attempted, namely that of prior coëxistence in the mind, has not altogether escaped the notice of philosophers. Dr. Brown, in more than one passage, advances the idea, that on a sufficiently minute analysis "all suggestion may be found to depend on prior coëxistence, or, at least, on such immediate proximity, as is itself, very probably, a modification of coëxistence." In order to this nice reduction, however, he adds, we must take into account "the influence of emotions, and other feelings that are very different from ideas; as when an analogous object suggests an analogous object by the influence of an emotion or sentiment, which each separately may have produced before, and which is therefore common to both." As illustrative of this, he refers, among others, to cases of remote resemblance; as when, "for example, the whiteness of untrodden snow brings to our mind the innocence of an unpolluted heart; or a fine morning of spring, the cheerful freshness of youth." In such cases, he says, "though there may never have been in the mind any proximity of the very images compared, there may have been a proximity of each to an emotion of some sort, which, as common to both, might render each capable, indirectly, of suggesting the other." The same principle he applies to suggestion by contrast, as when the sight of a person with a remarkably long nose brings to mind some one whom we have seen with a nose as remarkable for brevity; the common feeling in the two cases being that of surprise or wonder at the peculiarity of this feature of the countenance.