rejected the letter here." I cannot but think that he would have done better, if, instead of rejecting the letter which Flamsteed had retained, he had restored the original designation, both in this case and in that of y Scorpii.

Under the head 51 Libra in the "Cycle," Admiral Smyth emphatically says, "Flamsteed designated it & Libre, thinking he thereby followed Bayer; whereas in fact this star is & Scorpii: it con

sequently ought not to have been jumbled into the Balance." *

7. How Mr. Darby can affirm that he has "followed Mr. Webb's example, in omitting, with few exceptions, the epoch of the distances of the binary stars," passes my comprehension. I can only say that, in referring to Mr. Webb's book, I have always been struck with the frequent introduction of the epochs to which the particulars belong: and, on the contrary, in my cursory inspection of Mr. Darby's, I was as forcibly struck with the general absence of the epochs, even where they were most essential. One or two instances which I noted may suffice to show the kind of difference to which I referred ::

(1). Aquarii. DARBY. "Dist. 2"7, Smyth; 3"5, Bishop; 3"9, Dawes. . Must be widening, &c." [It is, in fact, closing. WEBB. "Dist. 3′′6, 1831; 2′′7, 1842." [On page 159, Mr. Webb informs us that "all data, not specially excepted, are taken from the Bedford Catalogue," in which therefore the quoted distances are found, the latter of which is probably about o" 5 too small.]

(2). n Corona. DARBY. "Dist. o"5. A very severe testobject, &c.-WEBB. "Dist. 1" more or less; less, 1859. One of H's severest tests. Smyth divided it, 1832; but could not always even elongate it, 1842."

Has Mr. Darby followed the example of Mr. Webb?-But, even if Mr. Webb really had committed the error of usually omitting the epoch of distance in cases of considerable variability, would not Mr. Darby have done far better by supplying the deficiency in his book, than by generally following so faulty an example ?

There can, I imagine, be no question that when a book is so entirely a compilation that the author does not consider himself responsible for the accuracy of many of the statements it contains, he is bound to specify distinctly the authority on which each statement rests. Whenever this is not done, the public may reasonably conclude that the author has verified its correctness:-but this, I fear, is rarely the case in the work under consideration.

The magnitudes of the stars seem to be taken from the "Cycle" of Admiral Smyth, who has taken care distinctly to inform us (vol. i. p. 427)—“ My star A [the brightest of the components of a double star] is invariably registered under Piazzi's magnitude, as I know that he took much pains on the subject," &c. In one striking instance, however, (that of y Corona,) an emphatic protest of the Admiral against Piazzi's magnitude (the 6th) has been entirely omitted by Mr. Darby, and also the further remarks upon it in the Speculum Hartwellianum : but as there is a special interest connected with that star, I may perhaps, with your good leave, advert to it in a separate communication to your valuable periodical." I remain faithfully yours, W. R. DAWES.

Hopefield Observatory, Haddenham, Bucks:

July, 1865.

* In a recent edition of the smaller Maps of the U. K. S., revised by Mr. Dayman, Scorpii has also the name 51 Libræ attached to it. This was not so in my edition.

THE MOON'S DIAMETER.

TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-As your note at the foot of Mr. Howlett's letter, in the Register for this month, is, I take it, an intimation that the discussion on the sun's diameter is now closed, I do not wish to transgress your rules by forwarding you further observations to substantiate my argument that the variable diameter of the sun is an optical illusion, produced by our surrounding atmospheric lens.

I now beg leave to draw attention to the apparent variable diameter of the moon and its corresponding apparent variable velocity, which, according to a series of direct observations, carried on for many years, proceed from optical illusions produced by our atmosphere. It is somewhat extraordinary that the various and changeable effects of our atmosphere have been so little considered in drawing conclusions on the apparent variable sizes and velocities of celestial bodies, when it is so well known that the atmosphere possesses the same properties as an ordinary lens.

Atmospheric refraction must necessarily affect all celestial observations, not only as regards the direction of the rays, but also the apparent size of the celestial bodies. Humboldt was struck with this appearance, and remarked, in his Views of Nature-"It is only under the equator that man enjoys the glorious spectacle of all the stars of the southern and northern heavens revealed at one glance. Some of our northern constellations-as, for instance, Ursa Majoris and Ursa Minoris-owing to their low position when seen from the region of the equator, appear to be of a remarkable, almost fearful magnitude."

The moon varies in its apparent diameter, according to its declination, from 29' 26", when seen in England at the highest altitude, to 33' 30", when seen at its lowest elevation in the meridian.

These atmospheric effects necessarily produce corresponding illusions in the apparent velocity of the moon, and also various distortions at low elevations, and thus render the question of the moon's apparent motion exceedingly perplexing to all astronomers. Formerly, Buckhardt's Lunar Tables were adopted in our Nautical Almanac; we have now Hansen's Tables-both founded on theory and computations. It is impossible to establish the laws of refraction by observations made in England. Had our atmosphere been composed of a series of concentric media of equal thickness, density, and temperature, and not subject to much variation, it might be possible; but this is far from being the case. At the equator, the atmospheric pressure does not vary of an inch from 30 ins. at the level of the sea all the year round. The aërial strata from the level of the sea up to 14,000 feet continue more or less, at the same elevation, of the same temperature, and the maximum amount of refraction is equal to the semidiameter of the sun when seen rising or setting in the horizon-viz. 16' 30", and not 33' as recorded.

I remain, Sir, yours faithfully,

EVAN HOPKINS.

15 Clarendon Gardens, W.

June 14, 1865.

The Astronomical Register.

OCTOBER.

No. 34.

1865.

ADMIRAL SMYTH.

ON the 9th of last month there passed from among us one to whom all amateur astronomers are greatly indebted, Admiral W. H. Smyth, dying as it were in harness-for he had but completed his work on Sidereal Chromatics the year before, and almost up to the time of his death was engaged in the compilation of a Nautical Dictionary.

Admiral Smyth was born in January 1788, and entered the Navy in 1805, serving with distinction in all parts of the world for a period of ten years. In 1810 he was appointed to the command of the gunboats in aid of the Spanish Patriots. He obtained his Lieutenant's commission in 1813; was made Commander in 1815; and in 1816 he joined Lord Exmouth in Tunis Bay, when abolishing Christian slavery. From this time until 1824, he was employed in making surveys in the Mediterranean, from which resulted a collection of charts of the greatest utility to navigation. In January 1824 he was made Post Captain, retiring from active service in 1825.

His energies were now given to the cause of astronomy; building an Observatory at Bedford, and devoting himself to the observations for the Bedford Catalogue—a work impossible to be too highly estimated, and for which he received the Gold Medal of the Royal Astronomical Society. Upon its completion he quitted Bedford, and shortly after went to reside at St. John's

Lodge, Aylesbury, where, amid a little circle of scientific friendsDr. Lee, the Rev. W. R. Dawes, the Rev. J. B. Reade, and others -he passed the latter part of his useful life. At Hartwell, close by, was the old familiar telescope he had so long used at Bedford, now known as the Hartwell Equatoreal; while he had in his own grounds the means of occasional reference to the heavens. Nor was he by any means idle: he continued the Bedford Catalogue in the Edes Hartwelliana and the Speculum Hartwellianum, and, as lately as the beginning of 1864, compiled an Addenda to the former work. In these handsome quartos, suggested by and printed at the expense of his friend Dr. Lee, the Admiral has collected together an astonishing variety of information on all kinds of subjects-astronomy, archæology, agriculture, numismatology, antiquities, history,—the reader must be hard to please who does not find here something to attract his attention.

The Bedford Catalogue has enrolled a numerous band among the disciples of Urania, and it may be justly stated that no work can be put in competition with it as an introduction to practical astronomy for the amateur. The happy style in which it is written seems to bring the young beginner and his guide into friendly personal relations. He tells him what to do, and how to do it; he anticipates difficulties; shows how they are to be surmounted; gives his experiences-the whole in language terse and energetic, and peculiarly his own. Should the subject be at all dry, a quaint story or curious anecdote draws the reader on, and before he is aware of it the difficulty is mastered. How well can we picture to ourselves the enthusiastic observer, in his large cloth boots and "Welsh wig cap, manoeuvring his paper squadrons of observations for the forthcoming Cycle! He loves the science and everything connected with it; and he does not lose sight of the fact that he is writing for those who not only love the science itself, but the means by which it is carried out. The second volume of the Cycle-the Catalogue-is a model of what such a work should be; for clearness of design, lucidity of explanation, and happiness of description, it stands preeminent as a list of celestial objects.

Admiral Smyth's published works commence in 1824, with a Description of Sicily. For a Descriptive Catalogue of Roman Medals, in 1834, he received a vote of thanks from the Numismatic Society; he also published a Catalogue of Roman Coins

belonging to the Duke of Northumberland, in 1856. In 1854 he published a work on the Mediterranean, which obtained the Royal Society's Gold Medal. He assisted in the translation of Arago's Popular Astronomy, and the same author's Lives of Popular Scientific Men; Benzoni's History of the New World, &c. He contributed papers of every kind to nearly all the Scientific Societies, and was a constant writer of interesting articles for the United Service Journal for a period of twenty years. He became a Fellow of the Royal Astronomical Society in the year 1821, and of the Royal Society in 1826. Want of space forbids us to enumerate the other Societies whose initials he was entitled to add to his name. He was made Rear-Admiral in 1853, ViceAdmiral in 1858, and full Admiral in 1863.

BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE.

REPORT OF THE LUNAR COMMITTEE.

I

The Report of this Committee, an account of the proceedings of which we gave in our number for July 1865, p. 186, was presented to Section A. by its Chairman, James Glaisher, Esq., F.R.S., who said that, when he accepted the post of Chairman, it was with the understanding that he should not take any actual part in the work itself— the real work had been done by Mr. Birt. He would, therefore, confine himself to the steps the Committee had taken in assisting Mr. Birt, by preparing Forms for registering lunar objects. Four Forms had been drawn up and printed, with the view of being used not only by Mr. Birt, but by other gentlemen possessed of telescopes who devoted themselves to this work; and even with such assistance many years' labour would be needed. Form No. 1 is intended to record the place where, the time when, the observer by whom, and the nature of the observations that are made, the telescope used, the estimated brightness of objects, and a column for a symbol of reference to each object observed. This, the Chairman said, constitutes the "Day Book" of the moon. Form No. 2, which we noticed in our number for June, p. 170, furnishes directions for posting from the "Day Book" into the "Ledger," which is Form No. 3. This is a very important form it contains columns for the positions, extent, height or depth, and brightness of specified objects, and references to existing authorities. Form No. 4 is intended to aid in the computation of the positions of objects which are situated near others, the localities of which are well determined. The Chairman spoke of the size