once been thoroughly familiar may be revived again in the memory, by striking the proper key-note in the music of old association, — at least if it be struck at a time when the mind is shut out from the disturbing influence of immediate practical interests, and temporarily imprisoned in the past. All this is in no way inconsistent with what we have been maintaining, — namely, that it is impossible to distinguish clearly in memory what you have never distinguished clearly even in direct knowledge, that you cannot surely recognize what you have never surely known. You may certainly have the most vivid recognition of things very long indeed forgotten, and as you would suppose, absolutely forgotten, supposing always that they were once thoroughly familiar, as almost every one must have experienced at times even in dreams. But then what is it that has apparently obliterated these familiar things from memory? It is the claim on the attention of a long succession of other duties and interests, and if these for a time be excluded, even though only by the images of a dream which diverts the mind into long-deserted tracks, there is no reason at all why the old attitude of mind should not be resumed, and when resumed, should not appear as fresh and natural as ever. Moreover, nothing is more likely to be suddenly revived in this way than a long-disused mechanical habit, with some old link in the chain of which the eye or ear suddenly finds itself again in contact. All experience shows that as nothing is so easy as to forget mere words and names, even when the things they represent are quite clearly before the mind, so the only way to recollect them is not so much to dwell on them, as to get into some well-worn groove of habit, by the help of which you come upon them unawares, in the midst of equally familiar words. Thus it has been noted that even people who suffer from that very serious disease of the brain called aphasia, almost always swear correctly, indeed say anything correctly which they are not trying to say, but which just completes a chain of old associations. Aphasic patients can scold the servants — an operation in which they are started, as it were, by a habit, rather than by a set purpose — when they cannot even get nearer to the word "moon" than to cal it "that public light," or to the word "card" than "cigar." Carried back into an old groove of habit, they will run straight, though if they were to pick their own way, they would go blundering from side to side. Thus the man who forgot his most intimate friend's name, when he wanted to introduce him, recovered it at once in the mere swing of the familiar imprecation with which he said, "Confound you, Robinson, what is your name?" But the ease of the process of recovering such a dropped stitch in the memory, if you can only go back a few stitches and come upon it with the momentum of an old habit, is no argument at all in favor of the proposition that complete forgetfulness is impossible. For the truth is, that a very great proportion of our lives is made up, not of habitual actions which come quite pat, but of half-perceived, half-discriminated, half-grasped circumstances, which we could not clearly recall the next instant, for the very excellent reason that they were not clearly presented to us when they were presented. Anything which the mind has once really made its own, it may recur to, even long after it had seemed to be obliterated; but what has never been its own when it was first in contact with our thought, cannot become so in memory. You may disinter a long-buried train of associations, as you may disinter an old Roman road long hidden by the superincumbent dust of ages. But then the train of associations must have been there, and must have been firmly welded together once, before it can be possible to disinter it. Great portions of our lives are unrememberable simply because they have never been vividly lived, and indeed, in all the minutiæ of their detail, hardly could have been vividly lived at all. If you don't know what you see at the time you see it, it is no great fault of the memory if you cannot remember it when you see it no longer.
Determination of the heights or clouds. — Mr. Alexander Ringwood, of Adelaide, has sent home a short paper on this subject, which appears to have been privately printed. He proposes to carry out the observations with a small simple altazimuth instrument. The principle is intelligible enough. The sun's altitude being known, and the edges of the projections of cloud shadows being parallel to the sun's rays: if we have a map of the country round the station, and mark on it the spots where the sun‘s rays strike through clouds, or where the shadows of clouds fall, the determination of the height of the cloud stratum is effected by plane trigonometry, if we observe the altitude of the precise points in the cloud.