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Jupiter, by Mr. S. B. Nicholson, in the table on p. 180 and on p. 181; but footnotes have been used for this addition, in order to keep the text nearer the original date. Possibly I have overlooked something in dealing with similar recent discoveries: Astronomy moves fast in these days, and it is not easy to keep the pace she sets.

The hypothesis of a Sunspot-swarm of meteors, given on pp. 200-206, has been added intentionally. At the time of the lectures it had only just been formulated, and although the picture on p. 205 was shown, little was said on the matter. Two years' consideration has strengthened my confidence in this interpretation of the facts known to us, without producing any objections of a fatal character; and it seemed to me therefore that, as I was writing a book, I ought to put it in; to omit it might be interpreted as a lack of confidence on my part. At the same time I do not wish to ignore the attitude of other astronomers, which is duly acknowledged on p. 205.

I have made every effort to acknowledge the source of the illustrations and to obtain permission for their publication where needful. But there may be some oversights. If so, I would beg the same kind consideration for the lecturer turned author as is extended to him from all quarters during his preparation of the lectures, immediately he mentions the magic words "Royal Institution" and "Children's Lectures."

H. H. T.

University Observatory,
November 10, 1915.