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at last recommended that a transit room should be built at the south-east angle of the mansion, where a meridian could be commanded at all times, from the lower passage of Capella on the north, to the southing of Fomalhaut : and in this I proposed that the moon and moon-culminating stars should be observed as regularly as circumstances would admit of, by means of a wellmounted five-foot transit telescope, albeit, but for such an exigence, I am averse to seeing so large a meridian instrument in the hands of an amateur.
The next point was, so to apportion the new structure that it should deform the aspect of the mansion as little as possible.: on communicating my anxiety on this point to my friend Mr. Bevan, of Leighton Buzzard, he declared that it would never look half so ugly as the green-houses he had seen against some of our best mansions; "and, after all,” added he, “who would listen to any one who could dare to decry building an observatory ?”
Early in 1831, I opened the trenches by drawing a meridian-line: my data were equal altitudes of the sun, taken with a well-adjusted reflecting-circle by Troughton, and an artificial horizon, and there was also the time by the portable transit. From this we raised perpendiculars to strike the angles of the south-east corner of the library wall, and, having stumped out the dimensions, dug down to the “live” rock for placing the foundation upon.
As we had but the single instrument in view, I was resolved that it should experience no derangement or tremors for want of solid supports, and therefore had a large mass of the best marle bricks joined with cement raised for placing the piers upon, with a good space between it and the walls for ventilation ; every care being taken to guard against damp, and a capacious dry drain laid around the building. The stone piers, each six feet high and cut from a single block of Portland stone, were then erected, and the flooring was carried so as not to touch them. This is the cross-section, from north to south :
* Poor B. Bevan, C.E. died on the 1st of July, 1833. The night of the lunar eclipse was his last : he rose from his bed and observed the commencement, but expired during the progress of the phenomenon.
Indeed I must confess that there was no sparing of materials in the construction, for, though the transit-room is only eighteen feet by twelve—sixteen feet in height outside and ten feet five inches inside—with an ante-room of eight feet and a half, there were nearly twenty thousand bricks used, reckoning four thousand five hundred to each rod of work. The flooring was laid to a level with that of the inner apartments of the house, and, the wall under the south-east intervening window being cut away, the observatory and library became as it were, incorporated. The ante-room is fitted for the keeping and trimming of lamps; and a flight of steps leads to its flat and well-leaded roof, on which a five-foot achromatic may be occasionally used.
From the form of the eastern portion of its wall, and the interior lockers fitted on the west, the transit-room is octangular in shape, with its centre cut by the north and south windows and the chax or slit through the roof from the north to the south horizontal points. I had made arrangements for the shutter which closes this, being counterpoised with weights, as in my own at Bedford ; but I one day found that a person had suggested lifting it by a crane-necked contrivance which I never could approve of, although good John May, formerly an armourer in the navy, had made it of most unexceptionable materials and workmanship. I submit a representation of it as a warning, because what is termed at sea an “Irish purchase” is shown by the position of the central pulley ; had it been a little lower, the cosine of the cord between it and the shutter would nearly have assumed the maximum state of helplessness. Even now, its chief action is that of battering the roof and shaking the ceiling.
During the time this room was under construction, Mr. Thomas Jones, of Charing Cross, was employed in getting the transit instrument ready, under my immediate inspection; and, as simplicity with capability for duty forms a very considerable point with me, in all mechanism, and the workmanship
, was limited to only what was necessary, it was soon completed. The telescope has an aperture of three inches and three quarters, and is sixty inches in focal length, two reading circles divided on silver and furnished with clamps and tangent-screws, with a full battery of eye-pieces, sliding plates for them, and rack-work motion to moderate the lighting-up of the lines within the telescope. It is borne at the centre by two well-proportioned cones, having a circumference of twenty-five inches at the telescope, which terminate in rigorously turned pivots of bell-metal of one inch and a quarter in diameter :