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made under the hypothesis of the undulatory theory of light. According to that theory, the diameters of the rings surrounding the spurious discs of stars are functions of the aperture of the telescope alone. Mr. Pritchard observed that the mathematical investigations were somewhat intricate, but that he hoped before long to offer to the Society a popular but logical demonstration of this phenomenon of the rings, bringing the subject within the comprehension of persons not possessing very extensive knowledge of analysis.
Mr. Dawes said that it was a curious circumstance that Steinheil maintained a very different view, and at the same time it was singular that his 8-in. object-glass at Leipsic would not separate $ Cancri, although its focal length was 12 feet.
Mr. Pritchard observed that, if that were really the case, the responsibility rested with the maker.
Mr. Dawes : Besides, a long focus will give a much better disc than a short one.
Mr. Pritchard : It is practically easier to correct chromatic and spherical aberration in a telescope with a long focus than in one with a shorter.
On Ġ Herculis, by Mr. Fletcher.—The observations of this star, with a power of 1,000 on a 9-inch object-glass of Cooke's (used by Mr. Fletcher), show that at present it is a single star. This was confirmed by Mr. Dawes last year.
Mr. Huggins then described the apparatus employed by him in spectrum analysis of the stars and nebulæ. The apparatus and large diagrams of the same were exhibited. (For some particulars of this, see Astron. Reg. No. 27, p. 61.) A beautiful spectroscope, on Mr. Huggins's model, for celestial observations, made by Mr. Browning, was explained by Mr. Huggins.-Mr. Browning stated, in answer to a question by the President, that the price of the instrument was 18 guineas, although one which would do the same work, but not so highly finished, could be made for 12 guineas.
Description and Photograph of Mr. Fletcher's Observatory and Equatorial, at Tarnbank, Workington..
On the Sun's Surface, by Mr. Brodie.- These observations were made with an object-glass of 81 inches aperture, by Cooke, 13 feet focus, Dawes's eye-piece, with positive power instead of single lenses being used, and occasionally a diagonal reflector with
Huyghenian eye-pieces. The whole surface of the sun appears to consist of a photospheric cloudy stratum, exactly answering to Sir J. Herschel's simile of a chemical precipitate settling down, the indentations giving the appearance described as mottling, willow-leaves, &c. Mr. Brodie had sometimes seen the ricegrains, so called, and compared them to a shingle beach: on one occasion he saw them uncommonly well through a red hazethey were very irregular, the sides of the ridges appearing remarkably steep; the indentations seemed to be about 2" in depth, and they were sometimes speckled with black dots or pores. He had observed the umbra of the spots take a wispy form. Mr. Brodie concluded by stating that he could perceive no interlacing of particles on the surface of the sun, and could not reconcile the willow-leaf theory with what he had observed.
Mr. Lockyer regretted that the paper he had promised to bring forward at this meeting was not ready; but regretted it the less as it would have been very similar to that already read by Mr. Brodie. What he wanted to call attention to was this that while Secchi said the solar photosphere was made up of clouds, Sir John Herschel stated his belief that it was composed of solid and permanent matter. Mr. Lockyer's observations tended to show that the matter was not permanent.—Mr. Chacornac was of the same opinion, and had been so for years.-Mr. Lockyer gave some particulars of an observation of the sun made during a fog, which enabled him to use a very high power. He had distinctly seen the formation, as it were, of several of the so-called willow-leaves, and had seen them turn round and gradually disappear.
Mr. Brodie wished to observe that, in his opinion, the appearances seen and described by Mr. Nasmyth were not the same as those called rice-grains, which could be observed with comparatively small instruments; while the former, Mr. Nasmyth stated, could not be detected unless with very powerful instruments and every atmospheric advantage.
The President said that as the sun was now being scrutinised in all quarters, it would be better to postpone any remarks on the present discussion until a future occasion; but he would call the attention of the meeting to what was doing with regard to the moon. He had examined Mr. Birt's work; but it would take one individual fifty years to complete what Mr. Birt had undertaken, and unless he had assistance it was a hopeless task. Co-operation was therefore necessary; and he asked the members who were accustomed to such observations to work in concert with Mr. Birt and the Lunar Committee in carrying on the necessary examinations and tabulating the lunar objects.
Mr. Dawes han ded in some sketches of a small portion of the sun's surface.
Colonel Strange rose to explain, and to controvert some observations made by Mr. Yeates, in a paper relating to a paper of his (Colonel Strange's) on transit instruments, and pointed out the difference between segmental and semicircular bearings for the pivots. [The paper by Mr. Yeates appears in the Monthly Notices for May; but as that number was not in the hands of the Fellows at the date of the meeting, June 10, it was somewhat difficult to follow Colonel Strange's explanation.]
The Rev. F. Howlett exhibited drawings of solar spots made that morning and the day before, and observed that, with reference to the theory of planetary influence on the spots, they generally increased or diminished together in both N. and S. hemispheres; but that at present an exception existed, as the northern spot was gradually diminishing, while a southern one was increasing and developing. Mr. Howlett further remarked that one spot generally struck, as it were, the key-note of the style of spots visible at one time. Thus, on the 8th inst. a fine group was a rude but grand triangle, with sides 60,000 miles long, and was made up of subordinate triangles a type of form frequently seen. The delicate features of the photosphere Mr. Howlett thought could hardly be delineated without the use of a screen, on which the beautiful granulated mottled appearance was seen with a 3-inch Dollond. It appeared precisely like new-fallen snow this morning, the forms being not rounded, but sharply angular.
The meeting, which was a very full one, was then adjourned to November.
LUNAR COMMITTEE OF THE BRITISH ASSOCIATION
FOR THE ADVANCEMENT OF SCIENCE.
A meeting of this Committee was holden on Thursday, May 11, 1865, at Dr. Lee's, 5 College, Doctors' Commons, London, James Glaisher, Esq., F.R.S., in the chair, when the Secretary, W. R. Birt, Esq., F.R.A.S., reported that the observations in which he has been
engaged during the last six years are still in progress, with the view of obtaining data for the formation of a catalogue of lunar objects, and the construction of a map of the moon on a sufficiently large scale to ensure accuracy in the insertion of details. For these objects Mr. Birt has 369 series of observations, both of a micrometrical and physical character. Of the micrometrical, the Secretary reported 821, which he had made during the interval (three months) between thé last two sittings of the Committee; some for the magnitudes of objects, and others for their positions. The last had reference to four groups, viz.: the Picard group, the Posidonius group, the Dionysius group, and the Friesnecker group,-each crater above named forming a central point from which angles of position are taken, and distances measured to fix the positions of surrounding objects.
Under the head “ Catalogue,” the Secretary reported the entry, in the forms provided by the Committee, of 192 objects since the meeting of the Association at Bath, making, with the 386 objects then reported, a total of 578 lunar objects now catalogued. The Secretary also reported that a skeleton map had been constructed at Hartwell, according to Dr. Lee's suggestion, with a view of exhibiting the sizes of the various craters when projected, and mapped from the data obtained from observation. The diameter of this skeleton map is 6 feet 3 inches, and the meridians and parallels at 5° and 10° are drawn in. The computation of the co-ordinates for each degree of the final map is being proceeded with.
The Chairman remarked that the Committee kept steadily in view the production of a map that should bear the closest investigation as to accuracy, particularly of the smaller details; for, although photography was undoubtedly a great assistance in lunar studies, time entered as an element in the production of the pictures—whereas the positions and sizes of objects which the human eye only can detect being determined by micrometrical measurement, we have a basis for accuracy of detail co-ordinate with the accuracy of the original measurements.
Thanks were voted to Mr. D. A. Freeman and Mr. C. Grover for assistance rendered by the communication of observations, and the Committee adjourned.
THE ROYAL OBSERVATORY, GREENWICH.—The Annual Visitation was held on June 3, the first Saturday in the month, as is customary. The weather was very threatening in the morning, but the clouds broke out in the afternoon. Amongst the company present, a very numerous one-were the Earl of Rosse, Sir E. Belcher, Dr. Lee, Mr. De la Rue, Mr. Huggins, Mr. Birt, Professor Tyndall, F.R.S., Sir D. Brewster, Mr. Hodgson, Mr. Cooke, Mr. Burr, Mr. Dawes, Mr. Whitbread, M.P., Mr. Brodie, &c. &c. The visitors' held a very protracted sitting, and our reporter was obliged to leave before the Astronomer Royal's annual statement was promulgated.
CORRESPONDENCE. N.B.-We do not hold ourselves answerable for any opinions
expressed by our correspondents.
DOUBLE STAR MEASURES. TO THE EDITOR OF THE ASTRONOMICAL REGISTER.
Sir,—Your correspondent “ B. A.” gives, in your last number, the result of some measurements of y Virginis, and asks for others for comparison, as well as for the positions and distances of the companions of & Bootis and 44 Bootis. I have, therefore, the pleasure of handing in the mean results of my operations on these three very interesting objects with my 93-inch achromatic :
, Virginis Pos. 164 só Dist. 4*132 Ep. 1865*37
186542 44 Bootis „ 240 4 9 4'554 » 1865-46 Your correspondent's distance of 5'•52 for y Virginis is evidently too large ; but I have generally observed that the larger and finer the telescope, and the better the circumstances, the smaller has been the resulting distance of a double star.
I am, Sir, yours very faithfully. Tarnbank, Cumberland :
ISAAC FLETCHER. : June 20, 1865.
BIELA'S COMET. TO THE EDITOR OF THE ASTRONOMICAL REGISTER.
Sir,-It may interest “B. A.” to hear that I saw Biela's or Gambart's Comet after it had separated into two portions in the end of 1845; and that I had an optical power of only 43, and an aperture of 2 inches. I did not see it in 1852, and it will be much fainter this year than before.
“B. A.” will find in Orr's Circle of the Sciences, article Astronomy, a catalogue of 198 calculated Cometary Orbits, with historical notices appended.
In return, perhaps “B. A.," who seems to have a good and wellmounted refractor, will be kind enough to inform me if, during the last or the present month, he has been able to distinguish the divisions of Saturn's rings. I have tried with a 61-inch glass and a power of 500, but could only fancy that I got a glimpse occasionally.
I am, Sir, &c.
TO THE EDITOR OF THE ASTRONOMICAL REGISTER.
Sir, The telescopic appearance and physical condition of the moon appears to be just now attracting considerable attention, especially as regards bright spots on its dark side : therefore, it is as