Just as the history of the stars and of the variations of the magnet is registered and posted up at the Greenwich Observatory, so is that of the compasses entered up here. Every compass that passes its examination may be said to receive its commission, and be appointed to a ship. Its number is taken; its vessel and destination are noted, and, subsequently, its length of service. On its return home from successive trips, it comes back to this place, when its character is again investigated and note made of any loss of magnetic power, of any deviations it may have exhibited, how it may have lost and how gained, and of any other circumstances showing either improvement or deterioration. Now and then one is blacklisted, but this seldom happens; the greatest loss yet noted being 30 minutes. The Standard Compasses cost, when made new, with tripod and all complete, 25_l._ each. After they have been some years in service afloat, they are sent into hospital for overhaul and repair. This costs generally 4_l._ or 5_l._, and they are then again as good as ever, and ready to guide another ship on her way over the mighty waters. The scientific part of the fittings of a ship of war, though of greatest value, are thus of lowest cost. A Standard Compass is, indeed, a beautiful result of human ingenuity. Generations of seamen and men of science have discussed the best form and materials, and the best mode of suspending the needle, that it may most freely and truly follow its mysterious love for the north. From the days of the old adventurers round the globe, to the date of the last voyages to the Arctic regions, successive sea captains have thought, and watched, and suggested, and the Standard Compass of the English Navy combines, it is believed, all that is best in all their thinking. After the Observatory was established, and one of its duties had been defined to be to pursue investigations on the deviation of the needle, it was thought desirable to have specimens of the instruments used in the war ships of other naval nations. With the open liberality that unites in brotherhood the scientific men of all countries, France and Denmark sent specimens of what their best men had succeeded in perfecting for the use of their navies. These instruments are very good, and attract deserved attention in the observatory-collection of specimens. The Frenchman is scientific, simple, and with an excellent contrivance for a moveable agate plane to avoid friction in the motion of the needle. The Dane is a good substantial instrument, even more excellently finished than the compasses issued to our navy.