The determinations of N.P.D. from July 2 to July 9, inclusive, are liable to some uncertainty, in consequence of the defective state of the clamp by which the declination-rod was attached to the polar frame. The determinations of R.A., however, are trustworthy. The R.A. and N.P.D. for July 2 are obtained by taking a mean between the results of the comparisons with (c) and (d). It is probable that in the observation of Nov. 30 the recorded micrometerreading was too great by 5 revolutions, and that the N.P.D. should consequently be diminished by 5' 43′′*2. = B.Z.478. 174753" Eq. Comparison. 275, 276 M. HOEK: Ephemeris of Proserpine. (Letter to the Astronomer Royal, dated Utrecht, 1862, May 20.) "Monsieur Kam a eu la complaisance de chercher la planète, de sorte que vous la trouverez aux endroits suivantes: 276,277 source whence I have obtained further information respecting the observation of Steinheibel. "In the Vienna Times of April 27th, 1820, there is to be found the following notice, communicated probably by my father: "Mr. Steinheibel, who for the last four years has daily observed the Sun and recorded his spots and faculæ with care in a diary, on February 12th (1820), at 10h 45m in the morning, observed a spot, which was distinguished from all the rest by its well-defined circular form, by its equally circular atmosphere, by its orange-red colour, and especially by its unusual motion, completing the diameter of the Sun in nearly five hours. As he made this interesting observation during a country excursion, it was impossible to have recourse to instruments or to communicate the phenomenon early enough to others; yet he is ready to answer fully every question put to him about this occurrence. It is very possible that a planet might be dis covered in this way, having its orbit within that of Mercury; and should the zeal with which Mr. Steinheibel has pursued this class of observations for a series of years, be rewarded by such a happy result, and lead him to publish his observations on the Sun, they would not be without interest for the public. "I have in a former letter incorrectly written the name 'Steinheibel,' according to Olbers, Steinhübel.' He lived for some time as Abbé at Vienna, and subsequently at Kremsmünster; at both of which places he occupied himself conti nuously with observations of the Sun. The above observation of his is given so differently to that of Starke, that I should consider it independent of the latter." "Si vous vouliez communiquer cette éphéméride aux astronomes Anglais qui pourraient s'y intéresser, vous m'obligeriez fort." Further Note on the supposed Observation of an Intra-Mercurial Mr. Carrington has been favoured with the following letter from Dr. von Littrow, which he hastens to communicate a translation of, referring at the same time to the Monthly Notices, vol. xx. p. 194. "Vienna, April 13th, 1862. "A fortunate chance has, at length, led me to-day to a On the Missing Nebula in Coma Berenices. By M. Chacornac. (Extract of a Letter to Sir J. Herschel, dated Paris, 22d May, 1862.) "Permettez moi de vous adresser quelques renseignements sur la nébuleuse variable dont vous annoncez la disparition dans le No. 6 du xxiime volume des Monthly Notice. "Le 19 Avril dernier, ayant dirigé le grand téléscope de M. Foucault sur la région du ciel environnant l'étoile (6) de la constellation de la chevelure de Bérénice, dans le but d'étudier la structure des nébuleuses qui s'y trouvent condensées; j' remarquai une nébuleuse double dont l'une des deux con posantes avait un éclat bien plus faible que l'autre, ce qu'il était facile d'apprécier par leur visibilité dans le même champ de 277, 278 Mr. DE LA RUE: on Heliotypography. Mr. Rümker has presented to the Society the manuscripts containing his Observations of Southern Stars made at Paramatta in the years 1826 and 1827. The thanks of the Council were voted to him for this valuable gift. On Heliotypography. By Warren De La Rue, Esq. The accompanying print of Sun-spots* was produced from a collodion negative, taken by means of my Newtonian reflector of 18 inches aperture and 10 feet focal length, on the scale of 3 feet for the Sun's diameter. The original focal image was enlarged before reaching the sensitive plate from about 1 inch in diameter to the scale of the picture, by means of a new combination of lenses which projects the image without sensible distortion on a flat field, and whose visual and chemical foci coincide perfectly. The camera which is attached to the eye-end of the telescope will hold a plate 18 x 18 inches, so that about one-fourth of the Sun can be depicted at one time. Even for a picture of such a size, the apparatus is very heavy, and could not be carried safely at one end of the tube, unless a provision had been made to support it. This is effected by means of a radius bar, which moves on a short independent axis, fixed on the framing of the telescope, in the prolongation of the polar axis. When Sun-pictures are taken, the telescope tube is for convenience rotated in its cradle through an arc of 90° from its ordinary position, so as to place the eye-piece underneath. To the sliding tube which carries usually the eye-piece, is fixed the instantaneous apparatus, which moves in a direction at right angles across the tube. The moveable plate of the instantaneous apparatus slides as nearly as possible in the plane of the primary focal image. The enlarged image is received at a distance of about 4 feet from the secondary magnifier. The printing block was produced by M. Paul Pretsch, according to a method he has invented. The process may be * See end of the volume.-ED. 278, 279 rendered sufficiently clear without revealing the exact process, which he does not wish to disclose at present. Gelatine is mixed with a salt of chromic acid, such as bi-chromate of potash, and poured on to a glass plate, and allowed to dry in the dark. If a plate so prepared is exposed to light, and a similar plate is retained in the dark, and the two plates are subsequently moistened with water, it will be found that the gelatine which has not been exposed to the action of the light will swell up like ordinary gelatine, while that which has been exposed to light will have become changed, and will remain unacted on by the water. If, therefore, an ordinary negative be placed over the dry prepared film of gelatine, and both are submitted to the action of light, the gelatine will become more or less changed in proportion to the intensity of the light transmitted through the several parts of the negative. For example, in the case of a negative of a Sun-spot, much light will pass through the image of the spot, less through that of the penumbra, and still less. through that of the bright parts of the Sun's surface, and the light so transmitted will produce a corresponding hardening of the prepared surface. When therefore the plate is subsequently moistened, the part corresponding to the spot will remain flat, more or less in proportion to the intensity of light which has acted on it, the bright parts will swell, and the gelatine film will represent the matrix of a surface-printing block. It is now only necessary to obtain, by means of known processes in electro-metallurgy, a counterpart of the gelatine. The plate so prepared is the printing block, which will furnish many thousand impressions at an ordinary printing-press, it being however necessary from time to time to clear the block, which is liable to become clogged on account of the want of depth in the light parts. On observing the impression at a little distance from the eye, a sort of mottling will be perceived on the bright parts of the picture; this is a true representation of the Sun's surface; on the other hand, an examination of the picture by means of a magnifier will show a vermicelli sort of granulation, which does not belong to the Sun, but results from the process and arises from the change which takes place in the gelatine film, passing as it were from the gelatinous or dynamic condition to the crystalline or static condition of matter. The grain may be made coarser or finer, and need in no way interfere with a picture more than the lines of a steel plate or the grain of a lithographic stone interferes with pictures engraved on the first or drawn on the second. |