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374 how to beget and perpetuate the best stock. Any thing that incites thought and action in this direction must advance agriculture and lay more deeply and broadly some of the foundations of national wealth. As Dr. Sturtevant's treatise is of this nature, and is eminently philosophical and scientific, it deserves well of all interested in this class of subjects. Its teachings, if generally understood, will lead to intelligent action in a line in which at present too much is left to lucky accidents.

1863 Sir John Herschel completed a descriptive catalogue of all the nebulæ and clusters known up to that time, the greater portion of which had been discovered by his illustrious father. Sir William Herschel, and by himself. This was a most valuable and complete compilation, and, although containing a list of no less than 5,079 nebulæ and clusters, it is singularly free from errors. This, no doubt, was in great part due to the careful and repeated revisions of the work by Sir John himself, and also to the fact that many lists of nebulæ existed with which Sir John's catalogue was constantly compared. No adequate idea of the amount of labor expended upon the preparation of this list can be given here, but a reference to the Introduction of that Catalogue must be made, where a concise account of the various revisions, collations, and comparisons, with the reductions executed (always in duplicate), extends over five quarto pages.

As the complete results of the observations of nebulæ were now accessible to astronomers in a convenient form, Sir John Herschel turned his attention to the formation of an equally complete catalogue of double stars. He proceeded assiduously with this work, and at the time of his death he had gathered data relating to over 10,000 stars, and had arranged these stars in order of right ascension, and had formed a synoptical history of all the known observations of about 4,000 of these.

This "Catalogue," in its imperfect state, was bequeathed to the Royal Astronomical Society, and volume xl. of their "Memoirs" contains the work completed in the form they have decided to give it, and for which the Society, jointly with the editors (who were but their agents), is responsible. So far we have given a sketch of the history of these two "Catalogues," gathered mainly from the respective Introductions. We propose briefly to indicate the shortcomings of the double-star catalogue, and we can do this best by comparing it with its predecessor in which Sir John Herschel's own plans were fully carried out by himself, and which naturally should have served as a model for the execution of the later catalogue. We will extract an entry from each of the two catalogues, and will explain these, so that an idea may be formed of the amount of information which can be had about any object contained in the two lists. The following extracts are made quite at random; the first from the "Catalogue of Nebulæ," the second from the "Catalogue of Double Stars:"

No. 2052; 688; I, 168; .... ; 10h 9m 498.9; $$+$$ 38.623; 1; 47° 53' 1".9; $$+$$ 17".83; 1; p B; v L; R; v g b M; 4.

No. 2052; h 698; .... ; 5h> 13m 488; 89° 6'; $$+$$ 38.09; $$-$$ 4".02.

The first entry relates to No. 2052 of the catalogued nebulæ, and we learn from it (taking the numbers in their order from left to right) that this nebula is No. 688 of Sir John Herschel's previous catalogue; is No. 168 of Sir William Herschel's Class I.; that no other persons have published any observations of this up to 1863; that its Right Ascension for 1860.0 is 10h 9m 498.9; that the annual precession in Right Ascension for 1880 is $$+$$ 38.623; that the number of observations upon which this place depends is 1; that its North Polar Distance for 1860.0 is 47° 53' 1".9; that the precession in North Polar Distance for 1880 is $$+$$ 17".83; that 1 observation was used to determine its position in North Polar Distance; and that this Nebula is "pretty Bright; very Large; Round; very gradually brighter in the Middle; and finally, that it has been