In my second paper on Automatic Registration, the means of obtaining a photographic register of the variations of the thermometer were briefly mentioned, and in the annexed plate a specimen was given of the register thus obtained; but as an apparatus possessing the requisites for practical application had not then been constructed, it may not be undesirable to those who are interested in the advancement of meteorological science, to know the means by which this object has been accomplished. A vertical revolving cylinder, and the carrying time-piece described in the above paper (see Plate VI. figs. 4, 5, 6, 7, 8), are mounted on a stand measuring 30 inches by 12, supported by four legs; the stems of the thermometer and psychrometer pass up through the table, and between the lenses and the adjacent surfaces of the cylinder; and the long cylindrical bulbs are sufficiently below the stand to be freely influenced by the currents of air, and at the same time to remain wholly unaffected by the heat of the lamps which are placed on wooden supports at each end of the stand, at such a height that the flame may be opposite the middle of the photographic paper on the cylinder. As it is impossible to superpose two registers of these instruments on the same paper, which may be done without inconvenience when the indication consists in a dark line, as in the photographs of the barometer and the magnetometers, the time-piece is so constructed that the hour-hand makes half a revolution in twenty-four hours. By this arrangement the two halves of the paper surrounding the cylinder give respectively a perfect diary of the two instruments. The glass cylinder is covered by a concentric cylindrical zinc case, having slits on opposite sides corresponding to the stems of the instruments, which are capable of being closed by sliding doors; by these means the cylinder, protected by its case, may be carried to or from the room in which the photographic manipulations are conducted, without any risk of exposure to light. The whole apparatus is also covered by a wind- and water-tight zinc case which rests on the stand, and is divided into separate compartments for the lamps by a partition towards each end, for the purpose of more completely isolating the thermometers from the heat produced by their combustion.