Many contrivances have been introduced to test the equality of compensation balances, but the majority have been abandoned from the circumstance that the heat was not equally distributed to the watches under trial. In pursuance of this object, an oven was invented, heated by hot water, which answers the desired end. It is an apparatus made of copper, two feet high, thirteen inches broad, and eight inches deep. From the top to the bottom, at the distance of fifteen inches, it is divided into two compartments. All around the upper one (except the front, which has a glass door through which the chronometers and watches are seen without opening it) is one inch of water. It has a chamber thirteen inches high, eleven inches broad, and seven inches deep for the reception of chronometers and watches. The water is introduced at the top in the same manner as a solar lamp is supplied with oil. The bottom compartment contains a jet of gas, which can at pleasure be regulated so as to keep the watch at any required temperature. The heat radiated from the inner surface of the chronometer chamber is thus equally distributed among the instruments under trial. A thermometer placed within the upper chamber indicates the temperature, and by this simple apparatus a watch can be regulated with the greatest nicety to suit the particular climate into which it may be taken. The DIAL AND HANDS should be sufficiently in contrast one to the other to show the time at a glance. Dials are sometimes made of gold or silver, but these are not so distinctly seen as white enamelled dials, with black figures or numerals, and dark blue steel hands; the enamelled faces, although, perhaps, more brittle than gold or silver dials, are therefore in greatest request. Up to a comparatively recent date the seconds' hand was placed upon the level face of the watch, but sunk seconds are now everywhere in use, even in the cheaper sorts of watches. The chief objection taken to the sunk seconds is that it disfigures the dial by breaking the uniformity of the numeral letters, the VI being of course obliterated to make room for it, but this obliteration seems of smaller consequence than the confusion which may arise from the use of longer seconds' hands and their being at any time mistaken for that of the hour or minute. The JEWELLING of a watch is an important part of its manufacture, inasmuch as it is by means of jewels that durability is chiefly secured. Watch pivots would rapidly wear out the metal in those parts in which there is continual friction, and jewelling has therefore become general. The watch-maker uses for his best watches a peculiarly hard kind of ruby, which has been known to withstand the wear and tear of the best part of a century without showing symptoms of yielding, whereas inferior jewels are perhaps scarcely so hard as the best tempered metal.