In 1885 nebular photography was commenced by _Isaac Roberts_ (1829-1904), the English amateur astronomer, who secured admirable representations of clusters and nebulæ. He published, in 1893 and 1900, two volumes of collected photographs of clusters and nebulæ. This monumental work was thus referred to by Dr _William James Lockyer_: “Dr Roberts has not only nobly enriched astronomical science, but has raised a monument to himself which will last as long as astronomy has any interest for mankind.” Perhaps the most remarkable revelation made by photography in this branch of research has been the discovery of the nebulæ in the Pleiades. In 1859 Tempel observed at Florence an elliptical nebula south of the star Merope. On November 16, 1885, the brothers Henry obtained at Paris a photograph of the Pleiades, revealing the existence of a small spiral nebula. This was confirmed by visual observations, and particularly by the photographs of Roberts, which also showed the entire cluster to be nebulous, and that “the nebulosity extends in streamers and fleecy masses, till it seems almost to fill the spaces between the stars, and to extend far beyond them.” In 1888 a further advance was made by the brothers Henry, who found seven stars to be strung on a nebulous streak. Since 1890 nebular photography has been pursued by Max Wolf in Germany, and by E. E. Barnard and J. E. Keeler in America. Wolf’s photographs of the constellation Cygnus brought out the close connection between the stars and the extensively diffused nebulosities discovered by him. In 1901 Wolf discovered a “nebelhaufen” or cluster of nebulæ, and in 1902 published a catalogue of 1528 nebulæ round the pole of the Galaxy, showing them to be systematically distributed. Keeler made his memorable observations with the great 36-inch reflecting telescope, which was constructed in England many years ago by Common. It afterwards passed into the hands of Mr Crossley of Halifax, who presented it to the Lick Observatory. With this great instrument Keeler commenced to take photographs of the heavens. On one occasion he photographed a well-known nebula, and on developing the plate was surprised to find seven new nebulæ besides that which he had photographed. On another occasion he exposed a plate to a nebula in Pegasus. He was amazed to find altogether twenty-one nebulæ included in the photograph. To give another instance, a plate directed to the constellation Andromeda contained no fewer than thirty-two nebulous objects. This has given an enormous extension to our knowledge of the nebulæ. But even this is not all. Keeler found on his plates numerous points of light which seem to be also nebulæ, either too small or too remote to appear as such. Apparently, however, they are not stars. Keeler’s work convinced him that, on a modest estimate, there must be at least _one hundred and twenty thousand_ new nebulæ within reach of the Crossley reflector. Half of these, he announced, were probably spiral.