With this figure in his mind, the telescope and the observer’s eye are poised in the opposite direction, through the window of the Observatory, towards a spot some half mile to the north, called Cox’s Mount; an eminence on which a wall has been raised to bear a numbered scale similar to that on the magnet—with this difference—that the one is very minute, and the other very large. To the corresponding figure on the distant wall the instrument is directed, and being thus pointed towards the true magnetic north, it is brought to bear upon the pivot of the compass—which by this time occupies a place on the top of the third pedestal to be tested. Without a complex description, and the free use of scientific terms, it would be perhaps impossible to convey a thoroughly exact conception of the steps of the whole process. Such a detail would be not only too technical, but unnecessary, here. It will be enough in general terms to say, therefore, that the indication obtained from a star, or from the instrument on the south pedestal, called the collimator, is, by means of the instrument in the centre, combined with a mark upon a distant object, and then brought down to prove the true powers of the compass placed on the third pedestal. It is a beautifully exact operation. The silence of isolation, the steadiness of stone tables and practised operators, the most beautifully constructed instruments, are combined to ensure accurate realities as a result. The tests are so varied, and so often repeated, that no error can escape, and the compass, when it leaves the building to begin its adventures afloat, commences its career with an irreproachable character as a Standard Compass of the Royal Navy—to be, on board the ship of war to which it is sent, a kind of master instrument of reference, by which ruder and cheaper compasses may be checked and regulated.