The nebula (on the horizontal A A) is seen surrounded by a dark space--at the end of a long dark lane or “rift” which reminds us of the track left by a snowball rolled along in the snow. Has the nebula in some mysterious way swept up the stars in its journey through space? We cannot at present either affirm or deny such interpretations. One or two of the brightest of the surrounding stars _might_ just be seen by an acute eye unaided by a telescope--but no more. The best existing telescopes would show _only_ the large nebular body on the line A A, and the larger white spots; the finest dust-like particles are stars of which the existence is only demonstrated by prolonged photographic exposures such as this, with a lens which focuses its image on to the _dry_ plate. The old “wet-plate” would not remain wet sufficiently long to “take” the picture. It should be borne in mind in looking at this picture that each of the minutest white spots is probably of at least the same size as our own sun: further, that each is probably surrounded by a planetary system similar to our own.] _Astronomy._--A biologist may well refuse to offer any remarks on his own authority in regard to this earliest and grandest of all the sciences. I will therefore at once say that my friend the Savilian Professor of Astronomy in Oxford has turned my thoughts in the right direction in regard to this subject. There is no doubt that there has been an immense ‘revival’ in astronomy since 1881; it has developed in every direction. The invention of the ‘dry plate,’ which has made it possible to apply photography freely in all astronomical work, is the chief cause of its great expansion. Photography was applied to astronomical work before 1881, but only with difficulty and haltingly. It was the dry-plate (see Fig. 12) which made long exposures possible, and thus enabled astronomers to obtain regular records of faintly luminous objects such as nebulæ and star-spectra. Roughly speaking, the number of stars visible to the naked eye may be stated as eight thousand: this is raised by the use of our best telescopes to some hundred million. But the number which can be photographed is indefinite and depends on length of exposure: some thousands of millions can certainly be so recorded. The serious practical proposal to ‘chart the sky’ by means of photography certainly dates from this side of 1881. The Paris Conference of 1887, which made an international scheme for sharing the sky among eighteen observatories (still busy with the work, and producing excellent results), originated with photographs of the comet of 1882, taken at the Cape Observatory.