after its emersion, is observed to change its colour*, and for many seconds to appear not only adhering to the circumference, but oftentimes projected on the disc, of the moon. Whether this optical deception is caused by an atmosphere surrounding the moon, or by the instrument used for the observation, or by what other means, I shall not stop to discuss but, as it is probable that its effects may be more discernible in those peculiar occultations which have been the subject of the preceding Memoir, it is desirable that the particular circumstances of the case in each occultation should be noted down as they occur; together with a de * Messier, who observed the occultation of Aldebaran on Sept. 25, 1755, states that just before the immersion, on the illuminated side of the moon's disc, he saw the star sensibly diminish in light, change its colour and become white: and that for 10" before its actual immersion it appeared adhering to the border of the moon. Con naissance des Tems, Année 1810, page 336. In a subsequent occultation of the same star, on July 11, 1757, he states that, just before its immersion, also on the illuminated side of the moon's disc, it appeared adhering to the border of the moon for 7", and afterwards remained 2′′ on the moon's disc, previous to its total disappearance: and that the star was easily discernible on the face of the moon by a reddish colour which it had acquired on approaching thereto. Ibid. page 339. + In the occultation of Aldebaran on July 5, 1755, Messier, with a 4 feet Newtonian reflector magnifying 140 times, saw the star for near 2" on the moon's disc: Le Gentil, with a refracting telescope of 6 or 7 feet, saw it adhering to the border of the moon, for 4" or 5" whilst Cassini, with his 18 feet telescope, saw it detached from the border, to the very moment of immersion. Ibid. page 335. : scription of the telescope used for the observation. Astronomers indeed now adopt the method of noting down the moment of apparent contact, as well as the moment of the disappearance of the star: and when it emerges again from behind the moon, they likewise note down not only the moment of its reappearance, but also the moment of its separation from the moon's disc. Indeed every remarkable phænomenon which may occur during any observation ought to be carefully registered: as it is only by a comparison of such cases that we can ultimately expect to discover the causes which influence or produce them. M. Cagnoli, in his Memoir, seems to have addressed his remarks chiefly to the principal observatories of Europe. But, however desirable it may be to have the co-operation of those scientific bodies, it is evident that many private individuals may do much towards accomplishing the object and design of the author. In many cases, they may perhaps be able to do more than can be effected in any fixed observatory: since they may be more favourably situated, on the earth's surface, for the observation, or may enjoy the advantage of a more clear and favourable atmosphere. Indeed, the greater the number of observers attached to this duty, the greater will be the chance of an accurate result: for, independent of taking a mean of the observations made near the same spot, we might be enabled to detect the errors of the lunar tables by means of simultaneous observations made in a favourable situation in a distant part of the world; agreeably to what the author has suggested in § 15 of his Memoir. In fact, by increasing the number of observers to an indefinite extent, over the whole surface of the globe, almost every occultation that occurs might be brought in aid of the method proposed by M. Cagnoli. In the present contracted state, however, of the science of Astronomy, we must confine our views to a more limited scale of assistance. In this country, indeed, there are many persons scattered throughout the kingdom who have the means and opportunity of making observations of this kind: and, amongst the numerous occultations which they observe, if they should find only one that belongs to that peculiar class of occultations, which is alluded to in the preceding pages, it would be a valuable discovery; and ought to be noted down accordingly, with all the circumstances attending it, in order that it may be compared with others of a similar kind. It is much to be lamented, however, that in this country there is no association of scientific persons formed for the encouragement and improvement of Astronomy. In almost all the other branches of the Arts and Sciences, institutions have been formed for the purpose of promoting and diffusing a general knowledge of those particular subjects; such as Botany, Agriculture, Chemistry, Anatomy, Geology, &c. &c. the beneficial effects of which are too evident to be insisted upon in this place. But, Astronomy, the most interesting and sublime of all the sciences (and, to our country, certainly the most useful) cannot claim the fostering aid of any society. It is however well known that many individuals, in various parts of the kingdom, have of late years erected and furnished private observatories at a very considerable expense. Nevertheless the utility of those establishments must be greatly circumscribed through the want of some mode of general communication amongst observers, by means of which their labours might be collected and registered; and thus rendered permanently useful. The formation of an ASTRONOMICAL SOCIETY would not only afford this advantage, but would in other respects be attended with the most beneficial consequences. It would induce many intelligent persons (who are at present restrained by want of due encouragement) to come forward as the patrons and followers of the science; and excite the more experienced to further exertions and new discoveries*. * The name of the Royal Society will naturally occur to the reader on this occasion: but that society was formed for the promo Although much has been already done towards perfecting our present system of astronomy, much still remains to be effected, both in theory and practice. Not only would the interchange of sentiments and remarks on the various celestial phænomena, which such a Society would afford, lead to the advancement of the science in general; but the comparison and discussion of the merits of the several instruments used for astronomical purposes would also tend either to their improvement or to the discovery of new ones. By means also of a society of this kind an active communication might be kept up with the principal astronomers in different parts of the world: and, thus, continual subjects of research or observation be submitted to public attention. The funds of such a society might likewise be usefully employed in the formation of an Astronomical Library, consisting of the most rare and valuable books on the science; and in collecting and transcribing the observations of astronomers in various parts of the world*. But, even without any views or pre tion and encouragement of science in general; and the subject of Astronomy appears to form but a small portion of its labours. Nevertheless the Astronomical Society would, in common with the Linnæan, Geological and other scientific societies, hope for the co-operation of its learned members. * The observations and remarks of many eminent astronomers, both ancient and modern, still exist only in manuscript, in the hands of private individuals; and ought, if possible, to be rescued from their present precarious situation, and deposited in a place of safety and |