DIRECTIONS FOR METEOROLOGICAL OBSERVATIONS, ADOPTED BY THE SMITHSONIAN INSTITUTION. THE following directions were originally drawn up for the use of the observers in correspondence with the Smithsonian Institution, by Professor GUYOT, of the College of New Jersey, Princeton, and are now reprinted, with a series of additions, for more general distribution. The additions are indicated by brackets, []. SECRETARY S. I, PLACING AND MANAGEMENT OF THE INSTRUMENTS. THERMOMETER. Placing. Place the thermometer in the open air, and in an open space, out of the vicinity of high buildings, or of any obstacle that impedes the free circulation of the air. It should be so situated as to face the north, to be always in the shade, and be at least from nine to twelve inches from the walls of the building, and from every other neighboring object. The height from the ground may be from ten to fifteen feet, and, as far as possible, it should be the same at all the stations. The instrument should be protected against its own radiation to the sky, and against the light reflected by neighboring objects, such as buildings, the ground itself, and sheltered from the rain, snow, and hail. The following arrangement will fulfil these requirements (Fig. 1): Select a window situated in the first story, fronting the north, in a room not heated or inhabited; remove the lattice blinds, if there be any, and along the exterior jambs of the window place perpendicularly two pieces of board (a b—a' b'), projecting to a distance of from twenty to twenty-four inches from the panes. At half this distance, ten or twelve inches from the panes, and at the height of the eye of the observer, when in the chamber, pass from one piece of board to the other two small wooden transverse bars (c d, c' d'), each an inch broad, for the purpose of supporting the instruments. Upon the outer edge of the boards fasten, in the usual way (H H), the latticed blinds which were removed from the jambs, or two others provided for the purpose. That blind behind which the instruments are to be placed, is to serve as a screen, and must be fastened, almost entirely closed, so as to make a little more opening; the other will remain entirely open, to allow a free access of air and light, and is not to be closed except in great storms. The whole must be covered with a small inclined roof of boards (B E), placed at least fifteen or twenty inches above the instrument. The lower part (JJ), or the basis, may remain open. [The foregoing is a convenient arrangement by which the observations can be taken without exposing the observer to the weather. To prevent radiation from the room, the windows during the intervals of observations may be closed with an inside wooden shutter. The outside of the lattice-work should be painted white, to reflect off the light and heat which may fall upon it.] Fig. 2. The thermometer must be placed exactly perpendicular, the middle of the scale being at the height of the eye against the two small wooden bars, so that the top of the scale being fixed by a screw to the upper bar, the bulb may pass at least two or three inches beyond the lower bar. The instrument is attached to the last by a little metallic clasp. (Fig. 2.) It will thus be placed ten or twelve inches from the panes, from the screen, and the other parts of the window. 1000 [In a later arrangement, a single transverse bar is used. This being placed at the necessary height, the thermometers are attached to it by small metal brackets, which support them at a distance from the bar of about two inches. The metal brackets are permanently screwed to the bar, and the thermometers are fastened to them by small finger-screws, by which they can be detached at pleasure. The order of placing them is shown in the cut.] Unless Reading. To read the thermometer, the eye must be placed. exactly at the same height as the column of mercury. this precaution is taken, there is a liability to errors, the greater in proportion to the thickness of the glass of the stem and the shortness of the degrees. The reading should be made at all times, and especially in the winter, through the panes, and without opening the window; otherwise the temperature of the chamber will inevitably influence the thermometer in the open air. The degrees must be read, and the fractions carefully estimated in tenths of degrees. After having rapidly taken the observation, another should be made to verify it. If there are several other instruments to observe, and the thermometer is to be read first, the first reading may be made some minutes before the hour; the second, after the reading of the psychrometer; and if there is a difference, the mean number is to be entered in the journal. When, notwithstanding the shelter, the bulb of the thermometer is moistened by rain or fog, or covered with ice or snow, it is |