Once inside the Observatory, the first impression is one of isolation and quietude. Look up to the wooden roof, and you see two shutters, to be opened when an observation is to be made upon a star. Through the floor rise three pedestals of masonry, built solidly from the earth, and isolated from the Observatory floor, so that no vibration may be communicated to them. All three stand in a row, running north and south. The object of two of them is to support with complete steadiness and truth two instruments for determining, at any moment of time, the exact magnetic north, whilst the third pedestal holds one by one the compasses brought there to be tested. The most northern of these three narrow stone tables is, in fact, a bed of trial—a place of ordeal—whilst the other two support the instrumental judges, who are to pass sentence upon the fluttering needles brought under their unyielding gaze. The test is a severe one. It is easy, with proper means, to get the true magnetic north with a fixed instrument on shore, but to make something that shall tell it with equal truth upon the deck of a ship, as it heaves and tosses, and plunges on the sea, is a very different thing. Yet, instruments equal to such triumphs of skill are obtained, and in this place it is that their qualities are first investigated. The south pedestal has upon it a tall tube of glass, within which there hang some long fibres of untwisted silk, supporting a magnetic tube so beautifully poised, that it obeys without let or hindrance its natural tendency towards the magnetic north. This tubular magnet has at one end a glass on which a scale and figures are engraved, but so fine and small as to be with difficulty seen by the naked eye. The second pedestal supports a telescope, with which the observer looks down the tubular throat of the magnet towards this tiny scale on the glass at its extremity. Our friends, the “spiders,” have contributed some lines to the telescope, and the centre one of these crosses the exact figure showing the magnetic position at the moment.