He has found fault with the site, but has pointed out none better (which is the real question), though repeatedly urged so to do.

He has heaped a great deal of abuse upon a very excellent institution, mainly, I believe, because he was not consulted about it, nor allowed to spend the pulic money on some costly whim of his own; and this he justifies by talking of his zeal for science and for the public good.

The only scientific point on which he has attempted to hold his ground is, a supposed defect in the present site; viz. that it does not afford the means of drawing a meridian line. I am willing to admit that, in my hurry, I did not develope Mr. Tayler's ideas clearly till the letter of May 3d. It is there shewn that Mr. Taylor confounded four different things, and quoted promiscuously authorities on each, applying to all the appellation of meridian line.

Now a meridian line has a meaning as definite in astronomy as a term can have. It is never used for a meridian mark, or collimating mark, but is a line drawn, as I have described in my letter, either on a large scale (when it is a part of a gnomon), or on a smaller scale, merely for a rough estimation of time, adjustment of buildings, piers, instruments, &c. There is plenty of room for a long line on the pier, but a gnomon would be of no real use; the smaller line can be drawn any where, but the object of such a line has been fulfilled long ago.

Mr. Taylor has attempted to retreat out of this difficulty, by saying he never meant such meridian lines as I have described. His authorities prove that he did. His first quotation from Lalande belongs to the ordinary meridian line, as the context shews. I cannot verify (for want of a reference) Mr. Taylor's quotation; and I cannot trust him for translating faithfully, or citing truly, but the passage clearly refers to the kind of meridian line thus described in Lalande, Astronomie, § 153; and, indeed, this may be the original to which he has alluded, such is the laxness of his citations:

"La ligne méridienne est le premier fondement d'un observatoire : la plupart des observations supposent une excellente méridienne; car c'est sur les hauteurs prises dans le méridien, et sur les passages au méridien, que sont fondées toutes les théories astronomiques."

This remark follows a description of the meridian line, such as can be drawn any where without astronomical instruments: Lalande's apparatus being "a small plate, with a pin-hole, raised on a stand seven or eight inches high."

Mr. Taylor now repudiates all idea of a gnomon. Why did he then, for he must be the scientific friend of the Liverpool Mercury, send the following answer to a correspondent ?—

"THE OBSERVATORY.-We are indebted to a scientific friend for the following answer to a correspondent :- The proposal of W. C. A., to have a meridian line traced for the port of Liverpool is one that naturally presents itself to all interested in navigation. By right such a line should be connected with the Observatory; but, unfortunately, the Observatory recently built, and now, as is said, in the course of equipment, is so placed that nothing of the kind can be done. The place chosen for it is an outof-the-way corner, without room for any one useful astronomical operation. The area of the Exchange presents a tempting place for the tracing of a meridian line, and were that disgusting monstrosity, called Nelson's Monument, removed, as it ought to be, a gnomon, with its accompaniments, would form an appropriate part of the construction.'

"Liverpool Mercury, March 7, 1845."

Again, if Mr. Taylor merely meant a meridian mark, and not a meridian line, how does his remark apply, that, on drawing such a line at the

Observatory, I must tumble into the river or the dock? A mark should be distinct, at a distance, and, of course, visible; but I never heard that there was to be a pathway from it to the telescope, nor did any one else, not even Mr. Taylor. When, therefore, Mr. Taylor says that in combating the meridian line I am tilting at a figment of my own, he lies, to speak mildly, under a mistake. It is, perhaps, an idle employment to explain his obscure meanings and shew their absurdity: but that a meridian line formed an item in his astronomical limbo is certain, both from his own language and from his authorities.

Immediately after quoting Lalande on the meridian line, he quotes him (§ 2606) on the meridian mark, evidently without any perception of the difference between the two. I give the passage with an extract from the preceding section:-" Dans un grand instrument des passages, l'axe étant bien horizontal, il suffit d'observer les passages d'une même étoile au-dessus et au-dessous du pole, pour voir si la révolution diurne est partagée exactment par la moitié. On remarque alors dans l'horizon, sur un mur ou sur un clocher, quelque point distinct, sur lequel on apperçoive le fil de la lunette; cet objet terrestre, placé dans le méridien, sert à reconnoître si la lunette ne s'est point dérangée, à la remettre dans le méridien en cas d'accident, à corriger, si l'on veut, à chaque observation, les petites inegalités que la chaleur aura pu y causer, ou du moins à en tenir compte dans les observations." Having thus shewn how to set up a meridian mark correctly by observation of a circumpolar star, Lalande goes on to explain how the instrument may be placed in the meridian by the transits of two known stars differing considerably in declination (commonly called the method" by high and low stars"), without any mark at all.

Biot, Astronomie Physique, liv. i. chap. 5, et seq., gets first a rough meridian line by equal altitudes of the sun, by which he places his transit: then adjusts by observation of a circumpolar star, and finally sets up marks for future reference. But he adds (note to section 79):- "On peut obtenir les mêmes vérifications par les seules observations astronomiques au moyen de la méthode indiquée, tome iii. page 130, Additions."

Perhaps Mr. Taylor may now find that Lalande, Biot, &c. are not quite so much on his side as he fancied them to be.

After citing Lalande on the meridian mark, Mr. Taylor quotes a much higher authority, Mr. Airy, but unluckily Mr. Airy refers to the collimation error, which is a different thing altogether. Mr. Taylor says, "The error of collimation is when the line of vision passing through the middle wire does not coincide with the mark set up at a distance to identify the MERIDIAN LINE. Now the error of collimation means no such thing. It is the angle which the optical axis of the telescope makes with the plane perpendicular to the axis of the pivots, and it may be discovered and corrected by observing a mark any where near the horizon in reversed positions of the instrument; the verification being analogous to the mode in which a carpenter or mason adjusts his square. If Mr. Taylor would learn the vocabulary of practical astronomy, he would not confound collimation error with meridian error, or a meridian line with a meridian mark. When there is a distinct mark near the north and south points, this will serve for ascertaining the collimation; and, indeed, there is no other use now made of terrestrial marks in the British public Observatories, though they go by the old name of meridian marks. But the collimation error can be as well got, in my judgment, by the stars, especially when the means of reversing are so manageable as at Liverpool, and the instrument itself so unchangeable.

Mr. Taylor quotes Bouvard, who mentions the use of meridian murks for collimation and meridian adjustment (in reply to my statement that Cassini and his school were the last persons who drew meridian lines for exact astronomical purposes), thus shewing that he was unenlightened as to the difference between line and mark. Accordingly, in my next letter, I

attempted to clear matters up, but with small success. Mr. Taylor gives up, indeed, his meridian lines, big and little, but still seems not to comprehend how a man can set up marks without actually drawing lines to them from the telescope. The Greenwich terrestrial mark is on the other side of the Thames. Maskelyne's old mark was, I think, on a chimney of the ranger's house. A deeper mist hangs over Mr. Taylor's intellect than ever settled on the trough of the Mersey, and there is no clearing off: he is “ a hazy philosopher of about the tenth magnitude."

In his last attempt on the meridian line (p. 37), Mr. Taylor drops his authorities, and utters several solemn dicta, which are all his own. Every body but he, the writers he relies on most (Lalande, Delambre, Biot), all say that you must set up your terrestrial marks by reference to pole-stars, especially Polaris. The transit is adjusted when (the axis being horizontal, and the line of sight perpendicular to the axis) the circle described by turning the telescope round passes through the pole. Now the line of sight passes through the pole when the upper and lower transits of Polaris differ twelve hours. There are some corrections to be applied to the star, which are known to astronomers by the names of Precession, Nutation, Aberration, and to Mr. Taylor by the very "vague" term of "algebraic assumptions; " but the variations of these corrections are perfectly well known, ten times better than well enough for the purpose. His babble about the "ecliptic," "nature of things," and "momentary motion," is nonsense and mystification, without any application mere Taylorism.

It is curious that, after all this ink shed, the Observatory is found to have a good south meridian mark, and a still better collimating mark, so that Mr. Taylor's objections are not merely silly in themselves, but not applicable. He is unlucky in his "guesses at truth.”

I have already shewn how unfairly Mr. Taylor twisted my explanation of what I meant by a "good horizon" into a definition of the strict astronomical meaning of "horizon," simply. In the hurry of answering by return of post, I took no notice of his quibbling (p. 26) on the phrase, "that the observer's meridian is the mean wire of his transit." Now, when it is said that the meridian passage of a star is observed, all that is understood or intended is, that the star has been noted at its passage over the mean wire of the transit. This sensible meridian is then reduced to the astronomical meridian by applying corrections, which are obtained from the level, from reversing, and from the observations themselves. If we limit the use of the words meridian and horizon to the definition on which strict demonstration is founded, new words must be coined or tiresome periphrases will be required in practical astronomy. Mathematically speaking, there has never been an observation made in the meridian or in the horizon, just as there is no straight line and no right angle actually existing; but, as Mr. Taylor is the only person who cannot or will not understand ordinary scientific language, there is, perhaps, no pressing necessity for alteration.

I have said the authors quoted by Mr. Taylor were not transit observers, which, if my words are to be understood literally, that they never used a transit, is not correct. Lalande was not a good observer (see note p. 70), and Delambre and Biot are best known as observers with Borda's circle. Their merits, however, are of a higher kind than that of noting phenomena. The countryman of Flamsteed, Bradley, Maskelyne, Pond, and Airy; of Graham and Ramsden, Dollond and Troughton, need not have cited foreign authority on observatories or transit instruments. It is precisely the branch of science in which we are most distinguished, and the volumes which issue annually from Greenwich and Cambridge, Oxford and Edinburgh, are, I believe, unrivalled.

APPENDIX.

No. I.

HALLEY'S COMET.

THE return of Halley's Comet in 1835 exercised the skill of many geometers, among whom Rosenberger, Pontécoulant, and Lubbock, are particularly distinguished for the extent and success of their researches. The heavens were carefully watched in accordance with their predictions, and, to the delight of every one, the Comet made its appearance very nearly at the time and in the place where it was expected. As soon as a sufficient number of observations could be procured, the elements of the orbit were corrected, and fresh ephemerides published. Dr. Rosenberger, who had already made the motions, of this body an especial subject of research, was most forward and most successful in these predictions; and in this country the superintendant of the Nautical Almanac applied the resources of his powerful establishment to the same interesting and important purpose. I believe I may assert, without being contradicted by any astronomer, that all possible assistance was afforded to them by this zealous and efficient officer. A few persons, indeed, unacquainted with the nature and difficulty of the problem, and not comprehending, moreover, the extent or nature of the assistance afforded, took upon themselves to criticise the superintendant and his ephemeris in the columns of the London Times. Among these would-be philosophers, Mr. John Taylor enrolled himself, and, though last in the field, he carried off the first prize of the Dunciad, against all competitors, named or anonymous.

I proceed to give an account of Mr. Taylor's performance, with extracts, and a few notes. His first letter is in the Times of Nov. 18, with the signature T., and is addressed to Lieut. Stratford, on his ephemeris of Halley's Comet. After some remarks on the discrepancies between Rosenberger's and Stratford's elements-elliptic elements be it remembered -the writer asks for the three precise and authentic1 observations, where and

There are no such things in astronomy as precise and authentic observations, in Mr. Taylor's sense; if there were, a few observations would be as good as a large mass.

2

by whom made, on which that calculation has been founded." A few words are added on the value of the 112 observations in the possession of the superintendant, and a suggestion made, that, if a publication of the whole be too onerous, the odd 12 may be given in the newspapers. An impertinent remark is then made on the Astronomer Royal (Mr. Pond), and, in conclusion, a claim is urged for "the three controlling observations to which the calculator of the orbit has trusted, and to which, according to the practice of astronomers since the time of Newton, the other 109 are to be considered subservient."3

In the Times of Nov. 20, Lieut. Stratford answered, that, being tired of anonymous correspondents, he would only reply to T. on being furnished with a name. And on Nov. 24, in the same paper, T. disclosed himself to be Mr. John Taylor, of 17 Bedford Street North, Abercromby Square, Liverpool.

On Nov. 27th, Lieutenant Stratford replied:

"I infer from Mr. Taylor's desire to know the three controlling observations to which the calculator of the orbit has trusted, and to which, according to the practice of all astronomers since the time of Newton, the other 109 observations are to be considered subservient,' that he cannot be acquainted with the method of obtaining accurate elliptic elements of a comet's orbit. The object in view is not, as Mr. Taylor seems to imagine, the derivation of parabolic elements from three observations, which, in the case of Halley's comet, would be utterly worthless, but the correction of the best existing elliptic elements; and, for this purpose, I have proceeded as follows:

*

*

*

"1. With Pontécoulant's Elements (Nautical Almanac, 1835, 1st edition, page 492), altering only the time of perihelion passage to Nov. 16-1935, Greenwich mean time, the position of the comet has been computed at each midnight from August 20, to October 31, 1835.

"2. With a small variation of each of the six elements in succession, and the other elements as in No. 1, six other ephemerides have been computed for the same period.

"3. Each of the six has then been compared with No. 1, and the effect produced on the right ascension and declination of the comet by a given variation of each of the elements has thus been obtained for the whole period.

2 The writer here manifestly wishes it to be believed that he could make some use of the Comet's places if he had them; yet that he really laboured under such a delusion is incredible. Perhaps Mr. Taylor will tell us how to designate the man who asks for what he cannot want as if he did want it, and who, by his manner of asking implies, and means to imply, an untruth, viz., that he intends or knows how to make use of what he has asked for, in case he should get it.

3 I need scarcely say that this is nonsense, and the writer would be grievously puzzled to find any authority for his dictum. If some observations are to be considered merely subservient to others, why make them at all? See the extract from Laplace, page 55.