[59] It is remarkable that nearly all the temporary stars have appeared in the region of the Milky Way.
[60] This expert comet-finder would appear to have more acute, sensitive vision on faint stars than Burnham (see ‘Monthly Notices’, vol. xlix. p. 354).
[61] Sir W. Herschel at first entertained this view, finding that with every increase of telescopic power more nebulæ were resolved. But in 1791 he said, “perhaps it has been too hastily surmised that all milky nebulosity is owing to starlight only.” Lacaille had remarked in 1755 that “it is not certain the whiteness of parts of the Milky Way is caused by clusters of stars more closely packed together than in other parts of the heavens.”
[62] This is exclusive of 47 new nebulæ discovered by Prof. Safford, which form the appendix to the catalogue.
[63] Chambers says only four examples are known, but this is erroneous, as Lord Rosse’s telescope has added five ring-nebulæ to the four previously catalogued.
[64] Some of the nebulæ in Messier’s list were discovered by Mechain at Paris, who, like Messier, earned celebrity by his cometary discoveries. He was born at Laon in 1744, and died at Valencia in 1805.
[65] O. Struve had expressed views identical with these in 1857 (see ‘Monthly Notices,’ vol. xvii. p. 230).
[66] Humboldt says this “name is evidently derived from the voyage of Magellan, although he was not the first who observed them.”
[67] I have selected the various objects in these lists from the New General Catalogue.
[68] These forms are more numerous than the annular nebulæ. They often exhibit a blue colour, and the spectroscope shows them to consist of gas.