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comets, and in adding three planets to our system: and under the able treatment of Lord Wrottesley, the second has produced a systematic measurement of numerous double stars, undertaken for the express and difficult
and difficult purpose of investigating the parallax of those awfully distant bodies.
For the benefit of enjoying an accurate opinion upon this matter, I have examined the telescopes of various observatories; and especially some of those which are termed German mountings, such as those of Mr. Dawes, Mr. Barclay, and Mr. Peters. But the strictest comparison I had was last spring in Oxford. It was on the occasion of my closing accounts with y Virginis, after attending pretty closely to her for twenty years. Having completed my measures at Hartwell on the 17th of April, 1830, I immediately started off for the Radcliffe Observatory, and arrived in time to get some observations of the same star on the evening of the 18th, with the grand heliometer by the brothers Repsold, of Hamburgh, which had just been got into good action by my energetic friend, Mr. M. J. Johnson. This was a severe trial of the powers of the Hartwell telescope ; for the heliometer is furnished with the best object-glass that Germany could furnish, and all the appliances attest the assiduity and care of Mertz and Sons. It certainly is a splendid instrument, with excellent optical definition, and is, no doubt, destined to render most important services to physical inquiry. Its object-glass is 7.5 inches in diameter, with a focal length of ten feet four inches: the scale is read by the illumination of a beautifully contrived application of Grove's galvanic heat upon a platinum wire; the appliances for manipulation are most conveniently arranged, and the clock-work driver of the hour-circle seems about as near to perfection as it need to be. But while thus rendering my meed of admiration to the Oxford heliometer, I I must still repose with confidence in the goodness and trust-worthiness of the telescope I have so long and, as I trust, pretty successfully used. The difference of mounting between the two instruments will be instantly apparent to the most unpractised eye, by examining Plate IX. and the following representation of the heliometer, drawn by Mrs. Smyth
A. Frame of the divided object-glass.
on the collars cc. D. Position circle, whose slow motion depends on ee, while the
clamp and tangent screws are ff. E. Microm. microscopes for reading off the interior scale at the
object end, illumined by galvanism. F. Rod for separating the object-glass. G. Iron box covering the declination axis. WW. Friction rollers for relieving this axis. H. Declination slow-motion bandle, and ss its screws. K. Rod for clamping the declination (the clamp itself is not
LL. Declination circle.
roughly set by the wooden handles.
To return to Hartwell. The equatorial-room is furnished with a chronometer compensated for sidereal time, and having a stop second-hand, with a leaping spring, for observing occultations and the like phenomena. There is also a simple and sonorous “journeyman,” which was constructed for the late Colonel Beaufoy, and can readily be put in beat with the transit-clock when required. The telescope adjuncts—as eye-pieces, micrometers, shades, fog-tubes, &c.—are the same which have been already described. The equatorial clockmotion invented by the Rev. R. Sheepshanks, and presented to me by him, is also fixed in this tower, with its governor preventing the jerking or grinding, which a vibratory pendulum would inevitably occasion; for, as the force on the train increases the velocity of the balls of the governor, they fly further out, and thereby increase their moment of inertia or resistance to motion. Mr. Sheepshanks called the adaptation a “conical pendulum,” because the rod of each ball describes a cone as it revolves: others designate it a “vertical pendulum,”—a case in which utrum horum, &c. is applicable.
§ 4. OF MR. EPPS'S MERIDIONAL OBSERVATIONS.
Towards the end of the year 1837, Dr. Lee engaged the late Mr. James Epps as his astronomical assistant at Hartwell. This gentleman had been for more than eight years the respected Assistant-Secretary to the Royal Astronomical Society, discharging his duties with uniform urbanity and intelligence; and, as he had for many years previously had charge of the chronometer-rating of a large marine establishment, he was considered to be fully qualified for carrying out the Doctor's wishes with regard to the moon-culminating stars. All the preliminary arrangements having been made, Mr. and Mrs. Epps were accommodated in Hartwell House from January, 1838, to the 10th of August, 1839, when he was suddenly taken ill, and died in his sixty-second year. He was buried in Hartwell Church, where Dr. Lee has placed an appropriate tablet with an inscription to his memory.
It will therefore be seen that Mr.
Epps was but a short time in his new situation : he entered upon its duties with ardour, and had so far acquired the esteem and regard of his patron, that Dr. Lee generously assigned a liberal pension to the widow.*
The geographical position of an observatory is always a matter of some interest, although a rigidly accurate determination of the several co-ordinates may be actually necessary only in those public meridian establishments where the absolute place of the moon has to be fixed. But, in compliance with the general rule, I had made a few observations for an approximate latitude and longitude so far back as April 1829; taking the altitudes of the Sun, Procyon, and Regulus with a rickety reflecting circle and an artificial horizon for the first, and establishing the second by two trips with a pocket-chronometer from my clock at Bedford. These were the results
Being satisfied that these conclusions would meet the existing wants, I rested on my oars; and in correcting any given quantity of time from the ephemeris, I usually applied one-eighteenth of an hour west of Greenwich as suitable to Hartwell, and as sufficiently near for all probable exigencies.† But when there was to be a regular observer employed, I suggested that a strong fusciculus of moon-culminators should be at once begun, for the twofold purpose of settling the longitude at home, as well as of aiding others abroad. This was complied with, though not carried to the required extent: yet a paper was drawn up and read to the Royal Astronomical Society in 1839, which, having taken place
* In January, 1845, Mr. John Glaisher, brother of the well-known Assistant Astronomer at Greenwich, was partly engaged to continue the Hartwell observations: he had just entered upon the regular routine, when he was most unexpectedly attacked with illness, and died, at the early age of twenty-seven years, on the 16th of May, 1846. lle had received his induction under Professor Challis, at the Cambridge observatory. His registered operations still await arrangement and reduction.
† In the folio volume published by Adams in 1700, intituled “ Index Villaris,” the position of Hartwell House is placed in latitude 51° 49' north, and longitude 0° 47' west of London.