On account of its greater sensitiveness the Lumière Sigma plate is recommended by Professor Barnard, although he draws attention to the fact that this plate has frequently been found defective in having small, round, transparent and opaque spots. It is also more subject to “chemical fog” than the Cramer or Seed. Otherwise, it is a beautiful and very rapid plate. When the comet is at its brightest, the Seed 27 Gilt Edge plates are recommended on account of their general freedom from defects and finer grain. With these few suggestions in respect to photographing comets, made by Professor Barnard in _Popular Astronomy_, No. 170, the amateur comet-hunter is enabled to make an attempt, at any rate, at photographing those wonders of the heavens which have proved so attractive on account of their varying appearance from night to night. For those who may not have a ready access to astronomical libraries, the above condensed account from Professor Barnard’s article on the subject should prove invaluable. In an account of his life-work given by Professor Barnard during the course of an after-dinner speech in January, 1907, at Nashville, and entitled by him, “Some Unastronomical Experiences of a Lecturer,” he referred to his interest in comets as follows: “I have always been interested in comets. These remarkable objects, which sometimes sweep across the heavens with their wonderful trains of light, and which in all ages have been objects of superstition and terror, are among the most interesting in the heavens. Little by little the mystery attached to them is being solved. This has been done mainly through the aid of photography. Many of the physical phenomena of the tails of comets are too faint to be seen with the eye, although it may be aided by a powerful telescope; but the photographic plate secures a permanent record of these in all their complexity and beauty. These photographs show that the form and other peculiarities of a comet’s tail are often utterly transformed from night to night. It is therefore highly important that a continuous series of photographs should be obtained of every active comet that can be observed, for their phenomena are as evanescent as smoke itself.