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while I was in South Wales, I did not happen to see the document. I understand, however, that it is somewhat anomalous in some of the clock-rate and azimuthal details, which probably require a further sifting. Still, most of the observations might, even in their present garb, be useful in a further series that may yet be made at Hartwell; for in those which Mr. Epps took for time, every attention was paid to the state of the instrument, namely, that it worked with no apparent error in collimation, and very little in level, but correcting for its azimuthal deviation as occasion might require. Except therefore the unavoidable errors of observation, and some trifling optical

, defects, it was concluded that nothing of importance could be urged against the mean of all the results.

Meantime Dr. Lee had a very long meridian-line taken and measured, which revived the question. This line commences near the wind-mill on Bledlow Ridge, runs due north through the transit-instrument at Hartwell, and trends onwards to Scots' Hill, near the ancient camp at Whitchurch.

. The whole is a length of about twelve miles (see plate I.), and a stout pole of forty feet in height was erected at each extreme: it was considered that from these stations, when their bearing and distance should be more accurately determined, the observatories of Oxford, Hartwell, Bedford, and Cambridge, might be geodesically connected, and afterwards carried from thence to Greenwich, the intellectual starting-point of the empire. It so happened that in the summer of 1842, my son Henry Augustus, of the Royal Artillery, then a cadet in the Military Academy at Woolwich, accompanied me to Hartwell, whither I was repairing to re-measure some sidereal objects.

On this occasion, the weather being very fine and having some leisure time, we made a correcting survey of the Hartwell grounds, and re-examined the long meridian-line. This was an opportune lesson for the youth ; for, though the theory of surveying is tolerably attained at the Academy, still there are many little matters of application and instrumental adjustment, which are perhaps only obtainable in actual practice. It was therefore merely a renewal of old habits in which I had formerly indulged to a considerable degree, and a light course of field-performance for my son.

It now struck me that as good a longitude for the Observatory as need be required, would be obtained by attaching it trigonometrically to Aylesbury Church-spire, the position of which in the great Trigonometrical Survey, as re-computed by Captain Yolland of the Royal Engineers from the original data, is

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In the first place, we carefully took the angles subtended between the principal objects of triangulation and the Whitchurch meridian-pole, with the seven-inch theodolite-carefully adjusted-standing on the transit-roof, and plumbing the centre of that instrument. The mean of the readings thus obtained were

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Joined by Mr. Akehurst, who had made the first measurements, and Mr. William Blake, we then went to the north meridian-pole, where we had good and distinct vision of all the necessary points, even to Bledlow Ridge, had we wanted them. The distance from the Observatory to the pole, as ascertained by Mr. Akehurst, is forty thousand two hundred and fifty-six links (0.66 to a foot); but I found it necessary, for the sake of commanding the angle, to measure back one hundred and fifty-six links on the meridian-line. station was therefore forty thousand one hundred links from the Hartwell instrument, where I found the angle between the latter and Aylesbury spire was exactly 17° 31'; and from Haydon Hill, ten thousand one hundred and

My

forty-eight links from the Observatory on the same line, the angle was 73° 50'. The question now was simply

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W, II, and O, being the base-line running from Whitchurch pole, through the Haydon IIill station, to the Observatory; and the apex is Aylesbury spire. We then have

Sin. WAO : sin. AWO:: WO : A0 =4.1008594 or 12614.2 links.
Sin. WAO: sin. AOW:: WO: WA=4.5387443 or 34573-6 links.
Sin. AHO : sin AOI :: A0 : AII=1.0348092 or 10834:5 links.

With these data, and assuming that in this latitude 62:83 feet are equal to a second in space, it follows that the longitude of the lartwell Observatory may be very safely regarded as in longitude 50' 39''16 west of Greenwich, or + 3m 22*:63 difference of time: and the latitude yielded by this method, is 51° 48' 11":58 north. There is a vague rumour that General Roy's data for the position of Aylesbury spire require correction : when this shall have been ascertained and reduced to a fact, there is no doubt but the corrective quantity will follow the inquiry, and be duly applied; then the same amount may be added to or subtracted from the ordinate for Hartwell. But until such an operation has been earnestly undertaken and satisfactorily performed, the trigonometrical longitude here given will answer every possible purpose, although mundane sphericity was not considered in the above computation.

To revert for a moment to the process by means of moon-culminating stars, I ought to have mentioned, that the vicinity of Hartwell is very strong in meridian means for attacking the problem, there now being no fewer than three other meridian batteries in immediate connection. The first of these is an excellent and efficient private observatory, erected by the Rev. J. B. Reade at Stone, and fitted with a fine transit-instrument on well-placed solid piers; and whose equatorial telescope is worked under my original Bedford revolving dome. The second is a neat transit-room built by the Rev. Charles Lowndes, at the Hartwell Rectory; it is furnished with a transit-telescope of 4.2 inches aperture, and six feet focal length, accompanied by a capital clock of Dent's. The third is a smaller one in Aylesbury, equipped by Mr. Thomas Dell. The last is well worthy of note, because it evinces the successful pursuit of practical astronomy under forbidding difficulties. Of less pretension than its costly neighbours, this Uranian room is but seven feet in length, five feet and a half wide, and six feet and a half high. It is constructed in the corner of a court-yard devoted to far different business, the turmoil of which has not prevented some excellent observations being made and recorded. By placing the pier for his thirty-inch transit and meridian-slit a good deal on one side of the room, Mr. Dell has contrived space for his clock and a writing-desk. The building is of wood, which, being screwed together, can be taken apart and set up again in a very short time, if necessary. The cost, including labour and materials, did not exceed six pounds.

The Hartwell transit-instrument is already described ; but, although not exactly necessary, it might have been interesting

it might have been interesting to mention that it resulted from a family legacy. The following inscriptions are engraved, on circular silver plates, above and below the transit cone's centre

This instrument was made by
Thomas Jones of Charing Cross, under the inspection of Capt. W. H. Smyth, R.N.

For the Transit Room at Hartwell, 1831.

Joanni Lee, LL.D.
Testamento Legavit Louisa Soror Carissima,

A.S. MDCCCXXXI.

Mr. Epps principally observed those objects which transited the meridian, as the moon, moon-culminating stars, and planets : but, having something to learn in using instruments of a larger size than he had been accustomed to, he can hardly be said to have fairly entered upon what was proposed to be his standard occupation. There are therefore some deficiencies and various awkwardnesses in his recorded observations, for which he could no doubt in some measure have accounted, had he lived to reduce them himself. Four or five years after his regretted death, all his rough registers were forwarded to me at Chelsea ; and, having closely investigated the whole of them, I selected three hundred and fifteen of his stars, many observed with the moon, by which to test the resulting right-ascensions, as a proof of their trustworthiness in questions of longitude. From the very tenor of this inquiry, it was attended with no small drudgery, as many were called that were not ultimately chosen. Every effort, however, was made to secure as great a number of the transits as possible from oblivion; but, owing to the instrumental corrections not being always noted, even the apparent clock-error was on many days too wavering to be depended upon. In this “fix,” probability has claimed its share of attention in selecting the Greenwich stars on which to append the corrections; and the squared sheets of paper mentioned in my Cycle (vol. i. page 429) were also called into requisition for describing the horological curve. In addition to which, a very efficient aid in these reductions was derived from computing a table of constants (sin. Z. D.--sin. P. D.) for every degree of polar distance, and applying the suitable correction to each star observed on that day; the azimuthal deviation constituting a most important element. In the following catalogue, the two Greenwich stars—high and low-selected for this object, are given in a column assigned for that purpose. The detail of one day's sifting compared with the orthodox work will, perhaps, be the best explanation of the adopted system ; since it was a case to which the more regular process of reduction was not altogether applicable.

By arranging the transits of each day in the order of their N.P.D. the increase or decrease of the clock-error shewed the rough azimuth deviation of

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