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Magnitudes,' &c., some distinct allusion was not made to the fact that that able and experienced astronomer, Rev. W. R. Dawes, was the working astronomer?" I answer, If "Bishop's Catalogue of Double Stars" be a misnomer, I am not to blame. I have literary sins enough of my own to answer for, and decline to be made a scapegoat for the sins of others. Nevertheless, after the information supplied in Mr. Dawes' letter in the Register of February, I shall gladly, if my book should reach a second edition, render "honour to whom honour is due." I have no doubt but that, if Mr. Dawes and Mr. Hind had lived in other times, their acuteness of vision, vigour of intellect, and accuracy of observation would have secured for them the honour of a place amongst the constellations; perhaps as the Aquila and Lynx of astronomical observers.

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2. The reviewer is at "a loss to understand how every turn of a pinion (or worm) working in a wheel of 360 teeth, fixed to the axis of the telescope, will move it one degree (p. xiii.).” The following is the quotation:- "If two wheels be attached, one a fixture on the polar axis, and the other on the telescope axis, each wheel cut into 360 teeth, then every turn of the worm which works in those teeth will move forward or backward one tooth-i. e. every turn of each handle will move the telescope one degree in right ascension or in declination." And it is added, in explanation, " In especial reference to this modus operandi, and in order to avoid confusion, the relative distances of the stars, one from another, or of the telescopic object from a certain star, are always expressed in degrees, or in parts of a degree, in the directions for finding the objects, both in right ascension and in declination." If the reviewer cannot understand that one tooth of a wheel, or circle of 360 teeth, corresponds with one degree of the heavens, I confess my inability to enlighten him.

3. The reviewer notices that "seconds of arc are sometimes misprinted for seconds of time." This typographical error occurs, I think, only seven times, and at the beginning of the Catalogue.

4. The reviewer points out another inaccuracy. "Dumbell,' too, is surely not the correct orthography of the familiar designation of 27 M. Vulpeculæ." If he had only looked into the Catalogue, under the constellation of Vulpecula, the proper place to look for it, he would have found that Dumb-bell was properly spelt, and have concluded that the instance which caught his eye in the tables was a typographical error.

5. The reviewer complains of "the lengthy list of corrigenda." That list amounts to just half a page; nothing deserving of severe criticism when the numerous details of 950 objects and the scanty time at the author's disposal are taken into account. I have seen a scientific work, recently published in London, in which the list of errata fills three pages. I charitably hope it will escape the notice of the reviewer.

6. Lastly, the reviewer finds fault with the plan and arrangement of my book, because, I presume, the matter given under each object is not tabulated. I reply, I made several efforts, and printed some sheets, to tabulate the observations under each object, and found it impracticable, from the large quantity of descriptive matter given under some objects. It would have doubled the size and the expense; so

that I differ in opinion here, also, with the reviewer. That eminent observer, the Rev. Dr. Robinson, of the Armagh Observatory, remarks, "The plan of your work is a good one, and will do good." I remain, sir, your obedient servant,

W. A. DARBY, M.A.

[We must take the liberty of correcting our correspondent. In our review we said, “We are at a loss to understand how every turn of a pinion, working in a wheel of 360 teeth, fixed to the axis of the telescope, will move it one degree!" The passage in our correspondent's book to which our remarks were directed we extract verbatim. "If two wheels be attached, one a fixture on the polar axis, and the other on the telescope axis, each wheel cut into 360 teeth, then every turn of the pinion which works in those teeth will move forward or backward one tooth; i. e. each turn of the handle will move the telescope one degree in right ascension or in declination, and, of course, half a turn will measure half a degree, the telescope axis wheel in the declination, and the polar axis wheel in right ascension." For the rest, we submit to our readers the work itself, our review, and our correspondent's reply.-ED. AST. REG.]

THE SUN'S DIAMETER.

TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir, I fully concur in the observations of your correspondent, Mr. Hickson-viz. "The appearances of the sun were so dependent upon the state of the atmosphere, that the sun might sink or rise either with an oval disk, or as a perfect sphere, from the varying effects of refraction." Again, "that the term observed, given to the tables, is, to some extent, misleading," not only to the public in general, but also to amateur astronomers, who are under the impression that the tables of the semi-diameters of the sun and moon have been derived from actual observations, and not from computations founded on theories.

Mr. Howlett on the morning of October 7. found the sun a perfect sphere, at an altitude of 16°, both the vertical and horizontal diameters being 32' 10".

In the afternoon of the same day I measured the horizontal diameter of the sun at an altitude of 20°, and obtained the following result:

Positive reading.

Negative

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32' 20"
30

32

2)64' 50"

32' 25"

In latitude 40° S., on June 2, three independent observers, by means of good sextants, gave a mean diameter of 32′ 22′′ at an altitude of 220, being 48" greater than the computed diameter recorded in the Nautical Almanac for that day.

To attempt to measure the diameter of the sun by means of the zenith distances of the limbs, instead of measuring the sun direct,

requires no comment. The mural circle and the transit instruments are not intended to determine the diameter of celestial bodies, but the apparent noon and polar or zenith distances. Hence, for this and other reasons, I look at the diameters lately recorded as derived more from computations and astronomical routine than from actual observations made to determine the question at issue, and therefore are not satisfactory. The table of the semi-diameter of the sun adopted in the Nautical Almanac has been computed by Bessel, but occasionally amended by the Astronomer Royal.

Mr. Howlett kindly intimated that I should hear again from him when the earth was in perigee. If Mr. Howlett has visited the southern hemisphere, and measured the sun by means of a good sextant, as well as a micrometer, I shall be happy to hear from him, so as to compare notes. My object has been, and still is, to arrive at the truth, and not make observations to suit any theories. Numerous observations, made during many years, in both hemispheres, have fully satisfied me that the apparent variable diameter of the sun proceeds from an optical illusion. If I am wrong, I wish to be corrected by means of satisfactory observations, made by independent scientific men, and not by mere remarks, grounded on preconceived I remain, sir, yours faithfully, E. HOPKINS, F.G.S.

notions.

15 Clarendon Gardens: February 11.

MANCHESTER LITERARY AND PHILOSOPHICAL SOCIETY.- The "Willow Leaves."-The following communication from Mr. James Nasmyth was read on January 24:

On June 5, 1864, between the hours of 11 A.M. and 2 P.M., I had the good fortune to observe, under unusually favourable circumstances, a large and remarkable group of solar spots. The willowleaf shaped objects forming the structural element of the entire photosphere, as also forming the details of the penumbral portions and bright margins of the photosphere overhanging the spots, were occasionally revealed with perfect distinctness; but the favourable moments for pure definition had to be watched for, by keeping the eye steady at the eye-piece and the hand on the focal adjustment, so as to be ready to make those minute adjustments that I find are requisite to meet the constantly varying condition of the atmosphere, which, especially during bright sunshine, is so fertile a source of defective definition, as is well known to practical observers. Some of the willow-leaf shaped objects were very favourably situated in an insulated position over the dark centres of the spots, and in that situation yielded me an excellent opportunity for carefully noting their exact form and proportions. In this respect I can with the utmost confidence pledge myself to the correctness of what I have_represented in the drawing which accompanies this communication. I continue to employ the term "willow-leaf" shaped objects, as sufficiently exact to convey to anyone a general idea of their form, and so to identify them. I might perhaps have hit upon some other term that would have been more exact and descriptive, and in that respect I was much

pleased with that which was employed by Mr. Stone, of the Royal Observatory, Greenwich, when he first beheld these remarkable objects by the aid of the great equatorial refracting telescope of the Royal Observatory, on which occasion Mr. Stone described them as "bright rice-like particles." Perhaps the more general term “lenticularshaped objects" would be better than either, as admitting of a certain latitude in respect to proportions, that may admit of a classification of any variety in these respects that future observations may supply. Any observer who, with due means at his command, is fortunate enough to obtain a satisfactory view of these truly remarkable structural details of the solar photosphere, can, of course, please himself as to the term that appears to him best to convey a correct idea of them. But the grand fact of their existence is now proved beyond all doubt; and they, as "a great fact," will ever remain so long as the sun exists.

CORRESPONDENTS' QUERIES AND REPLIES.

WATER ACTION ON THE MOON.-The extremely precipitous character of the lunar mountains generally, and the wonderful abruptness with which very many terminate on the lunar plains, without signs of circumjacent detritus, are alone strong arguments against the possibility of either water or atmosphere being in existence on the moon's surface, and thus forming so great a contrast to the mountains on the earth, where the action of the elements is so strikingly visible.

F. B.

As it seems undesirable that the pages of the Astronomical Register should continue to be so freely open to the "Lunar-Rotation Controversy," thus necessarily excluding more important matter, and as the settlement of the question seems as distant as ever, it has occurred to me that your subscribers' dissatisfaction may be appeased, and your controversialists' cacoethes allayed and gratified, were you to set apart some additional space at the end of your ordinary matters, as an appendix, where those who should still wish to carry on the argument might have the liberty of inserting their contributions (subject of course to the approval of the editor) by paying the cost of printing, at per page, in proportion to the quantity of space they might occupy. The cost could not be very considerable, and I think you would find some who would gladly avail themselves of the privilege. E. J. [Our correspondent's suggestion is a very good one. We hope to mature a plan by which it may be carried out: probably in our next number.-ED.]

THE PLANETS FOR MARCH.

Mercury passes from Aquarius to Pisces during the month, but is not favourably situated for observation. It arrives at superior conjunction on the 17th. It may, however, be seen in the evenings at the latter end of March.

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Venus is now a splendid object for daylight telescopic observation, her northerly declination being very favourable for this purpose. We have given her time of meridian passage in the Tables of Occurrences, as the smallest transit instrument will show her. She passes from Pisces to Aries during the month.

1st R.A. I 37 55 31st

3 8 22

Dec. N. 12 49

23 15

Diameter 24" 8

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luminated portion of the disc of Venus=0*405.

36" 21

Mars is in Taurus at the beginning, and Gemini at the end of March. It continues to decrease in size, and, although still very brilliant in the evenings, is losing all interest as a telescopic object. 1st R.A. 4 57 25 Dec. N. Diameter 7" 2

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Illuminated portion of the disc of Mars=0.897. Jupiter is in Sagittarius during March, and may now be observed in the south-east in the mornings, but his low altitude is unfavourable for the observation of so brilliant a planet.

1st R.A. 17 42 45

31st

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Saturn is now coming into view, following the bright star Spica Virginis, about half an hour of right ascension, and about a degree above the parallel of that star. Every possible opportunity should be taken of observing this planet before, like Jupiter, its altitude becomes so low as to render its observation difficult.

1st R.A. 13 55 10

13 48 55

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Dec. S. 8 57
8 17

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31st Dimensions of ring:-outer major axis, 42"1; outer minor axis, 11"4. Uranus, like Mars, is still to be observed; it comes into conjunction with the latter planet on the 22nd.

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The following are the Minor Planets which will arrive at Opposition this month. Full particulars will be found in the Supplement to the Nautical Almanac for 1868.

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