Since the apparatus of Mr. Brooke for the self-registration of the magnetic changes has been in operation at Greenwich, the time of Mr. Glaisher and his assistants has been more at liberty for other branches of their duties. These are numerous enough. Thermometers and barometers have to be watched as well as magnets. To these instruments the same ingenious photographic contrivance is applied. The wooden building next to the magnet-house on the south-west contains a modification of Mr. Brooke’s ingenious plan, by which the rise and fall of the temperature of the air is self-registered. Outside the building are the bulbs of thermometers freely exposed to the weather. Their shafts run through a zinc case, and as the mercury rises or falls, it moves a float having a projecting arm. Across this arm is thrown the ray of prepared light which falls then upon the sensitive paper. Thus we see the variations of the needle and the variations in heat and cold both recording their own story, within these humble-looking wooden sheds, as completely as the wind and the rain are made to do the same thing, on the top of the towers of the Observatory. The reward given to the inventor of this ingenious mode of self-registration has been recently revealed in a parliamentary paper, thus:—‘To Mr. Charles Brooke for his invention and establishment at the Royal Observatory, of the apparatus for the self-registration of magnetical and meteorological phenomena, 500_l._’ Every year the invention will save fully 500_l._ worth of human toil; and the reward seems small when we see every year millions voted for warlike, sinecure, and other worse than useless purposes. Photography, however, cannot do all the work. Its records have to be checked by independent observations every day, and then both have to be brought to their practical value by comparison with certain tables which test their accuracy, and make them available for disclosing certain scientific results. The preparation of such tables is one of the practical triumphs of Greenwich. Many a quiet country gentleman amuses his leisure by noting day by day the variations of his thermometer and barometer. Heretofore such observations were isolated and of no general value, but now by the tables completed by Mr. Glaisher, and published by the Royal Society, they may all be converted into scientific values, and be made available for the increase of our weather-wisdom. For nearly seventy years the Royal Society had observations made at Somerset House, but they were a dead letter—mere long columns of figures—till these tables gave them significance. And the same tables now knit into one scientific whole, the observations taken by forty scientific volunteers, who, from day to day, record for the Registrar-General of births and deaths, the temperature, moisture, &c., of their different localities, which vary from Glasgow to Guernsey, and from Cornwall to Norwich.