remarkable was a short and rather thick dark line near the North Pole, distinctly seen and depicted on Nov. 14th, at 12h. G.M.T., but on no other occasion (see drawing No. 10). Also on Nov. 10th the northern extremity of the narrow strait above mentioned was obscured, while from the distinct appearance of other features it might be expected to be well seen. On the contrary, a remarkable instance of permanence even in colour is afforded by a part of the coast to the north-west of the curious forkshaped bay, which was noted in 1852 as being "always particularly bright; " and on Nov. 20th, 1864, the same part is described as "remarkably white."-(See drawing No. 8.) CORRESPONDENCE. N.B. We do not hold ourselves answerable for any opinions expressed by our correspondents. THE WILLOW LEAVES. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-In Mr. Brodie's paper on the Sun's Surface, as given in your extracts from the Transactions of the Royal Astronomical Society in your last number, the following remark occurs: "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." In reference to the above remark, I should think that those who have had a favourable opportunity to observe these "rice-grain particles, which Mr. Stone so graphically described on the occasion of his first observing them as forming the structural element of the solar photosphere, will not be disposed to agree with Mr. Brodie. On a recent visit to Rome, I had the pleasure to pay my respects to Father Secchi, in company with Otto Struve. On our entering the Observatory, we found him at work on a model representation of the solar photosphere, which consisted of a black board thickly scattered over with oat-grains! Father Secchi at once remarked, "That is what I see as to the structure of the sun's surface." I leave those who take a special interest in this subject to draw their own conclusions, as to whether or not the objects, and on the occasion of their first discovery described as willow-leaf-shaped bodies, are the same as those described by Mr. Stone as bright rice-grain-like particles, or the oat-grains employed by Father Secchi in his model. Give them whatever name is most appropriate, the great fact remains that they are the true structural elements of the solar photosphere, and as such worthy of the most careful study as the immediate agents of the light-yielding powers of the sun, and most probably of the stars also! I am yours most respectfully, JAMES NASMYTH. Penshurst, Kent: July 12, 1865. . MERCURY. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-Will you permit me to enquire how near to Inferior Conjunction Mercury may usually be seen with refractors of moderate size, say of 4 or 5 inches aperture? Temple, E.C.: July 12, 1865. I am, Sir, your obedient servant, BRIGHT SPOTS ON THE MOON. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir, I do not know if Mr. Grover intended his communication in your July number of a bright spot seen on the dark side of the moon, as illustrative of my inquiry as to the identification of such objects. Should it have been so, Mr. Grover has certainly failed: he tells us that it was at the east foot of the Alps, very near the wedgeshaped valley, and that Schröter picked up a similar object very near the same place, September 26, 1788. Upon referring to Beer and Madler's map, I find the east foot of the Alps very near, indeed close upon the west rim of Plato. I suppose therefore that, leaving this position out of Mr. Grover's description, and comparing the proximity of the spot to the wedge-shaped valley with the engraving in Webb's "Celestial Objects," the spots seen by Schröter and Mr. Grover may have been in position near each other. Mr. Grover does not say how long he saw his spot; Schröter observed his for a quarter of an hour, but failed to identify it with any known spot. Now this is what, it appears to me, we want: not only the placing on record the appearance of a bright spot on the dark side of the moon, but so determining its position by measurement, if possible, that its place can be found on the day-side of the moon. Surely, if a spot of the kind were shining by strong earth-light, it should also shine brightly by sun-light. The round black shadow found by Schröter seems to be an exception to this, and it appears very difficult to conceive that a volcano in active eruption could give sufficient light to be detected at the earth's distance. I believe Herschel was mistaken in this respect, and the following consideration appears to be fatal to it:-Volcanoes, when in active eruption, are generally covered by a dense cloud, composed of various elements; such a cloud would, in all probability, reflect considerable light in the day-time, and a subdued diffused light by earthshine very unlike a little speck of light, similar to a star. I fear I have trespassed too greatly on your space; but can you, while on this subject, allow me a word or two more? I have met with several recorded instances of points that have been seen, glittering like stars, for a short time on the day-side of the moon, evidently dependent on the rays of the sun striking at the proper angle on a bright and probably crystalline substance, just as the rays of the rising and setting sun light up with great brilliancy distant panes of glass: snch glittering points are of course capable of identification. Are the two instances, given by Schröter and Mr. Grover, of a similar character on the night-side, but which fail of identification on account of erroneous estimated positions by the observers? Even measurement may fail in this respect, on account of libration altering the apparent position afterwards. July 12, 1865. JUVENIS. P.S.-Should Mr. Grover not have contemplated identification with a known object (Schröter's is not of this class), he has added one to a short list of curious and problematical objects. DOUBLE-STAR MEASUREMENTS. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-As the comparison of measurements of remarkable double stars by different observers may be interesting to some of your readers, I send you a few which I have lately obtained; some of the stars being the same as have been observed by Mr. Fletcher and Mr. Knott, and inserted in the Register for July and August. The observations were all made with an 8-inch refractor by Cooke & Sons; and a filar micrometer by Dollond, power 558, was used in all the measures excepting one set of 8 Serpentis, which was obtained with a double-image micrometer by Amici. A few remarks on some of the results may perhaps be useful. Cancri, A, B.-The disks perfectly separated. By some experiments, it was found that with a 7-inch aperture the disks were in close contact, and that a 74-in. aperture was required to produce a real separation. Cygni.-Small star, well seen, and the measures obtained without difficulty. If my whole series of measurements is not egregiously in error, the elements of Herr Behrmann, given in the Astron. Nachr., No. 1517, must be far from correct. The ephemeris he has derived from them gives, for 1865, P = 320° ± ; D=0′′4±. According to my own measures, the distance has scarcely varied for the last 25 years, while the angle has retrograded about 34°. The following are a few of my epochs : 1841.89 P= 23.75 D=1'667. With Mr. Bishop's 7-in. by Dollond. With a 7-inch by Alvan Clark. With an 84-inch by Alvan With an 8-inch by Cooke & Having usually seen the small star as well as could be expected under the atmospheric circumstances, I have no other than a negative opinion to give respecting the suspected variability of its brightness. Bootis.-All my measures of this star point to a very slow increase of the angle. Two or three epochs will show this: My distances between 1841 and 1859 are decidedly smaller than they were ever before or since. I am not aware of any reason for this. I remain, Sir, yours faithfully, Hopefield Observatory, Haddenham, Bucks: W. R. DAWES. August 14, 1865. DOUBLE-STAR COMPANIONS. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-May I be allowed to enquire whether any of your correspondents have noticed that some of the companions to larger stars, although of apparently the same size as other small stars similarly placed, require very different eyepieces to enable the observer to see them? Some seem to me to require high magnifying power to bring them into view, while others can only be seen with low powers. It may be that some of your correspondents have noticed the same thing; and if so, perhaps they will be kind enough to inform me what is the cause of it—that is, what reason can be given why stars of the same size, and as near as may be in the same relative position to the larger star, should require such different means as to magnifying power to bring them into view. It may, I suppose, arise from the quality of the light of each individual star: at all events, there is no other explanation that suggests itself to me, and I have been induced to call your attention to the subject, as I think that many stars have been missed by various observers in consequence of their not having examined the larger star with the right eyepiece. There is a small star in the double double 13 Piazzi in Lyra, R.A. 19h. 4m., Dec. 37° 43' N., which seems to require a strong eyepiece to bring it out with a moderate-sized telescope. It lies between the two pairs, about equidistant from both, rather "preceding " them, or about the same R.A. as the preceding star of the northern pair; and as it is not mentioned by Admiral Smyth in the "Cycle," it may perhaps be new to many amateurs. I found it in 1862, with a telescope of 3-inches aperture and a high eyepiece. The five stars form a very interesting object. Not far from it is a star, 17 Lyræ, to which I see there is a remark attached in my note-book, that the companion is better seen with a moderate power than with a high one. In the other double double, viz. ɛ Lyræ, I can see the seven stars, including the "Debilissima Couple," very distinctly with my 3-inch lens and a pretty high power; whereas in the star 94 Ophiuchi, called in the Cycle 7 mag., and the companion 13, I can see the small star well with 90, by glimpses only with 130, and not at all with higher powers. Perhaps it may be thought that the state of the atmosphere at the time of observation was not suitable to the use of high powers; but while that may be the case at times, I allude above to stars viewed as nearly as possible under the same conditions as to weather, magnitude of both stars, and the distance of the companion from the larger star. August 11, 1865. I am, Sir, yours respectfully, REFLECTING TELESCOPES. OBSERVER. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir, I beg to thank Mr. Dawes for his letter in the June number of the Register. Regarding the separating power of telescopes, I quite believe that on the aperture alone depends this power; but, of course, in practice a great deal depends on the perfect correction of the object-glass or mirror; and a long-focussed glass or mirror being more easily well corrected, would generally in practice divide the best. I have to thank Mr. Jones for giving me the distance of some close stars. The measurements are certainly of some standing; but it is not everyone who, like Mr. Dawes, has the means of giving very recent ones. The eyepiece I chiefly used was a Huyghenian of Mr. Cooke's make, which was an exceedingly good one. I had also a microscopic eyepiece giving upwards of 500; but the small lenses were not centred, and so the eyepiece was not to be trusted. Nights are few and far between which unite a perfectly clear and steady air with no wind; and with no observatory and a light stand, where high powers are used, the absence of wind is as necessary as good air. The weight and mode of suspension of Sir John Herschel's telescope gave him, I should fancy, as far as wind was concerned, all the advantage of an observatory. The other evening, with a new eyepiece, power of 550, I could clearly see the companion of Cygni-no easy star for a reflector. I was rather astonished to see it so well, for I have found with |