The photogravure[12] of the Trifid nebula, which accompanies this article, was made from a photograph taken with the Crossley reflector on July 6, 1899, with an exposure of three hours. It was not selected as a specimen of the work of the instrument, for the negative was made in the early stages of the experiments that I have described, and the star images are not good, but rather on account of the interest of the subject. At the time the photogravures were ordered no large scale photograph of the Trifid nebula had, so far as I am aware, ever been published.[13] The remarkable branching structure of the nebula is fairly well shown in the photogravure, though less distinctly than in the transparency from which it was made. The enlargement, as compared with the original negative, is 2.9 diameters (1 mm = 13´´). The fainter parts of the nebula would be shown more satisfactorily by a longer exposure. LIST OF NEBULÆ AND CLUSTERS PHOTOGRAPHED. +----------------------------------------------------------------------+ |N.G.C.| [Greek: a]|[Greek: d]| Remarks. | | No. | 1900.0 | 1900.0 | | |----------------------------------------------------------------------| | | h m s | ° ´ | | | 185 | 0 33 25 | +47 47.3 |H II, 707 | | 205 | 0 34 56 | +41 8.2 |H V, 18 | | 221 | 0 37 15 | +40 19.0 |M 32 | | 224 | 0 37 17 | +40 43.4 |Great nebula in _Andromeda_ | | 247 | 0 42 3 | -21 17.9 |H V, 20 | | 253 | 0 42 36 | -25 50.6 |H V, I | | 524 | 1 19 33 | + 9 1.0 |H I, 151 | | 598 | 1 28 12 | +30 8.6 |M 33 | | 628 | 1 31 19 | +15 16 |M 74 | | 650 | 1 36 0 | +51 4.0 |M 76 | | 891 | 2 16 15 | +41 53.6 |H V, 19 | |1023 | 2 34 8 | +38 38.0 |H I, 156 | |1068 | 2 37 34 | - 0 26.3 |M 77 | |1084 | 2 41 5 | - 8 0.0 |H I, 64 | | ... | 3 41 | +24 |_Pleiades_ in _Taurus_ | |1555 | 4 16 8 | +19 17 |T _Tauri_ and Hind's variable nebula | |1931 | 5 24 48 | +34 10.1 |H I, 261 | |1952 | 5 28 30 | +21 57 |Crab nebula in _Taurus_ | | ... | 5 30 | - 5 |Great nebula in _Orion_ | |1977 | 5 30 27 | - 4 54.2 |H V, 30 | |2024 | 5 36 48 | - 1 54.3 |H V, 28 | |2068 | 5 41 37 | + 0 0.8 |M 78 |