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THE HORSESHOE NEBULA IN SAGITTARIUS.
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mature death is the more to be regretted, as he was, so far as I am aware, the only other recent observer who has given himself with the assiduity which the subject requires to the exact delineation of nebulæ, and whose figures I find at all satisfactory, expressly states that both the nebulous knots were well seen by himself and his coadjutor Mr. Smith on August 1, 1839, i.e., two years subsequent to the date of my last drawing. Neither Mr. Mason, however, nor any other observer, appears to have had the least suspicion of the existence of the fainter horseshoe arc attached to the [eastern] extremity of Messier's streak. Dr. Lamont has given a figure of this nebula, accompanied by a description. In this figure [our Fig. 4], the nebulous diffusion at the [western] angle and along the [western] base-line of the Omega is represented as very conspicuous; indeed, much more so than I can persuade myself it was his intention it should appear."
When Lassell mounted his great four-foot reflector at Malta, lie devoted much of his time to a systematic review of those nebula; which had previously been figured either by himself or by Rosse and
Fig. 5.—Lassell, 1862.
others, and, as was expected from the excellence of the climate, the superiority of the great telescope and the skill of the observer, this series of drawings at once took its place among the acknowledged classics on this subject. Too much praise can hardly be given to Lassell for confining his attention principally to objects previously figured, and for resisting the temptation to roam in those fields which
