TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-If the above list of more or less difficult objects, well seen at Mentone during last winter with a 4-in. refractor, by Cooke, is of sufficient interest for publication, I shall be glad, as by eliciting comparison with other instruments, it may afford instruction as to what is to be expected from achromatics of this small aperture. The magnitudes and distances are as given by Mr. Darby. The 5th star in the Trapezium was frequently seen by me this spring, and, on two occasions, the 6th star was very distinct. The debilissima couple in Lyrae was readily visible on all fine nights, even in bright moonlight. Among Saturn's satellites, Rhea, Dione, and Tethys, were almost at all times readily visible, and not the less so when the planet was near to the full moon, and on a few occasions in April I had a good view of the inner or dusky ring. I was not able to separate ♪ Cygni, or 32 Orionis, nor could I ever see the 12th m. star, said by Mr. Darby to form one of the components of 14 Auriga. Mr. Webb (Intellectual Observer, iii. 58), writing of the star p. the lucida in σ Orionis, describes it as a minute star, and says that there is some suspicion of variability. I found it by no means inconspicuous on February 11, in full moonlight. 535 Argo Navis, marked on the S.D.U.K.'s large map as a nebula in R.A. 7:46 and S.D. 38.5, is a considerable and exquisite cluster of minute stars; and, in (about) R.A. 734 and S.D. 37°30, there is a singularly red star in a fine field. I think it must be 190 Argo. Temple: June 10, 1865. I am, Sir, your obedient servant, VARIABILITY OF BRIGHTNESS IN LUNAR SPOTS. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-Your correspondent, Mr. Ingall, has favoured lunar observers with some further observations of the interesting spot IC-2 west of Picard (see my letter in the Ast. Reg., Dec. 1864, pp. 295, 296). May I trouble you with one or two further remarks bearing on the variability of its reflective power. From the date of my letter, November 2, 1864, I have not seen the white cloud-like appearance which I frequently observed in 1859 and since. My attention having been called to the spot again by Mr. Ingall's letter, dated October 17, 1864, and published in the Ast. Rey. for November 1864, p. 264, I have frequently noticed it and taken measures both for its magnitude and position; and when I have been thus engaged, it has generally appeared to me small and faint, hardly coming up at any time to 6° or 7° the brightness which Mr. Ingall estimated it at on October 16, 1864: indeed, on some occasions it has been so faint as scarcely to exceed in brightness the adjacent surface of the Mare Crisium, rendering its measurement very difficult. On the morning of July 10, 1865, I intended to take further measures, but was prevented by clouds. It was then certainly not more than 1° brighter than the nearest part of the Mare Crisium, and I estimated it at 4°. It was also very small, by estimation between 1" and 2′′. The certain absence since October, 1864, so far as my observations extend, of the white cloud-like appearance which exceeded Picard in size the reduction of the pit-like marking to 1"-its range of reflective power from 4° to 10°-and a crater, or perhaps craters, having been seen on its site since October 1864-are all most interesting points; and if they are unable to bring home the certainty of physical change, they at least advertise us that an alteration of some kind in the reflective power (apparently independent of the angles of incident and visual rays), first of a surface as large or larger than Picard, and secondly of a point very much smaller, has actually taken place of late, and that this change may be limited by the period extending from Ápril 1859 to July 1865. Hartwell Observatory : I am, Sir, your obedient servant, ON THE MUTUAL CONVERSION OF MEAN SOLAR TIME AND SIDEREAL TIME UNDER DIFFERENT MERIDIANS. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-As the important but simple operation of converting sidereal time under one meridian into mean time under another has been erroneously explained by Mr. Darby, in the Introduction to his Astronomical Observer, and, as we are informed by him, is erroneously performed in some private observatories in his neighbourhood, may I be permitted to say a few words on the subject? Your correspondent ARCITENENS has rightly said that the difference of longitude is expressed in sidereal time, and requires to be reduced into mean time when mean time is sought; but in both the examples of working the problem which he has given he has applied the correction twice over, and has thus produced a result erroneous to the same amount as Mr. Darby's, but in the opposite direction. To avoid the possible occurrence of errors in the enormous mass of reductions of the observations made at Greenwich, the Astronomer Royal has provided tables for these reductions in which all the quantities are additive, and thus, no doubt, excludes many chances of mistakes which are peculiarly apt to occur to some computers in performing subtraction. But in the small operations of amateur observatories the use of the common tables of acceleration and retardation found in most collections of tables, and in some works on practical astronomy, are far more simple and quickly applied. The most handy which I am acquainted with are in Schumacher's Sammlung von Hülfstafeln, in which the reduction is given at once to every tenth of a second; and, by a very simple mental process, to the hundredth of a second. But those in Baily's Astronomical Tables, or in Galbraith's Mathematical Tables, and many other works, are almost as handy. As examples of the most simple method I will take the quantities proposed in Mr. Darby's Introduction, which I have already adverted to. EXAMPLE I. To convert 14h. 45m. sidereal time at Manchester into Greenwich mean time, on 13th July 1864: Manchester S. T. d. h. m. S. 1864, July 13 14 45 0'00 Add longitude of Manchester, West. .+o O 8 52'00 Greenwich S. T. Subtract sidereal time at preceding Green- O 14 53 52'00 O Sidereal interval since Greenwich mean noon=0 G. M. T., or mean time interval, since Green- 7 26 28.55 7 27 23'45 O O I 13'29 -O 7 26 10'16 EXAMPLE II. To convert 7h. 26m. 10°168. mean time at Greenwich into sidereal time at Manchester: The figures required for the conversion of intervals of sidereal time into mean time, and the converse, are not set down in Mr. Darby's examples, otherwise the great difference of the two methods in respect of labour would appear much more clearly. I remain, Sir, yours faithfully, Hopefield Observatory, Haddenham, Bucks: July 13, 1865. CONVERSION OF SIDEREAL INTO MEAN TIME. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-In a letter in this month's number of the Register, Mr. Darby states that the method of converting sidereal time at Manchester into Greenwich mean solar time, given by him in the Introduction to his Astronomical Observer, "has been in use for some years at three observatories in Manchester." I do not know what observatories Mr. Darby refers to; but as there appears to be an impression that one of the three must be Mr. Worthington's observatory, at Crumpsall Hall, in which the transit instrument belonging to the Manchester Corporation is mounted, and doubts will thus arise as to the accuracy of the time indicated by the Manchester Town Hall clock, I trust you will allow me to state that in the method employed in this observatory, the correction depending upon the difference of longitude between Greenwich and Manchester is always introduced. Your correspondent "Arcitenens," while rightly pointing out that Mr. Darby has neglected to reduce the difference of longitude to mean time, appears, nevertheless, to have very confused ideas on the subject, as he adds a correction which is not required, and then gives two methods of his own, both of which are wrong. In the first he has erred by subtracting 1468. from G. M. T. of preceding sidereal noon, and afterwards using a corrected value of the longitude; and in the second by adding 146s. to G.S.T. at preceding mean noon. The true Greenwich mean solar time corresponding to 14h. 45m. sidereal time at Manchester on July 13th, 1864, assuming a difference of longitude of 8m. 528., is 7h. 26m. 10'168.-I am, Sir, yours faithfully, JOSEPH BAXEŇDELL. Cheetham Hill, Manchester: TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-In the July number just to hand, article "Conversion of Sidereal into Mean Time," does not "Arcitenens" make a mistake in his example (ii.), in blending his longitude 8m. 52s. with his M. S. T., and then taking out his mean time equivalents from the sum of both ? h. m. s. Corresponding to 14 45 o'o sidereal time at Manchester, Mr. Darby appears to omit his correction for longitude (1°468.) FRANCIS M. MOORE. Belfast: July 4. THE BEDFORD CATALOGUE. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-In answer to numerous enquiries which from time to time have been made in your columns, as well as through other channels, in reference to a new edition of the Cycle, a brief statement may be of some interest to your readers. Admiral Smyth, whose name will ever be honoured by every amateur astronomer, has laid on my shoulders the grave responsibility of preparing a new edition of that most admirable work; but the prelude to its appearance is the re-observation of every object in the Bedford Catalogue with a 9-inch refractor of 12-feet focus. As many of the objects demand several epochs, and as it has been determined to give no results resting on single night's observations, it is obvious that time must be liberally granted for such an undertaking. Many circumstances have combined hitherto to prevent my making that progress with the work of re-observation which I earnestly wished for; but it is now steadily and systematically in hand, and in due time will, I trust, be brought to a satisfactory conclusion. I feel the responsibility of the duty entrusted to me, as well as the great honour of being connected with such a work as the Cycle, and in this spirit I shall do my best to meet the just expectations of the astronomical public. Tarnbank, Cumberland: I am, Sir, yours faithfully, ADJUSTABLE v. ADJUSTIBLE. TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-As questions of this nature are not unlikely to arise occasionally, it would be well, as one of your correspondents observes, could we lay down some general rules for their settlement. May not the following suffice? If the root of the word be French, or Italian, or what-not, would it not be courteous, and probably correct, to adopt the French or Italian method of spelling the derivative? In the present case it would be ajustable, and consequently adjustable. If the root be unquestionably English, our rules would require the derivative to be spelt with an a, as we have scarcely any such words spelt with an i, all of them being compounds of able or ability. But even should any such word not be traceable to a Latin root, we shall yet doubtless be compelled to adopt it in Latin; and then the question will arise, Of what conjugation shall it be? Naturally, as a rule, we should make it of the first, which would require a. All words signifying capability, are, in Latin, compounds of the particular root and the word habilis or habilitas. Almost a lion's share of these belong to the first conjugation; as, habitabilis, from habitari habilis; habitabilitas, from habitari habilitas: credibilis, from credi habilis, is an example of the third. Johnson gives both addable and addible, thereby plainly showing his notion of the law for English words. I may add, as an illustration of the rule, eatable -edible. Juxtâ would perhaps be the more likely Latin root for the word adjust, both as to sense and sound. While on this subject, I may observe that as meridionalis is strict Latin, meridional can hardly be wrong; but meridianus is equally so; and as we use meridian and not meridion, meridianal would seem to be more in accordance with English usage. It is curious that Johnson should have omitted the word appreciate; but he spells depreciate with c, giving at the same time depretiare (Latin) as the root; whence it may be inferred that he would have spelt appreciate with c: yet he spells negotiate with t, giving as root both negotium and négocier. So that truly "There is no rule without an exception." E. J. |