25. In all reports and bulletins posted or furnished to the press for publication, due credit must be given to the telegraph company over whose wires they were received. At all stations ordered to make river-reports, the depth of water above low-water mark will be observed at three o'clock (local time) each afternoon.

The sixth space in first line of Form 5 will be used for the depth in feet whenever the number exceeds eight, and the sixth space in second line for the odd inches. Whenever the depth does not exceed 8 feet, the word "River" will be used to fill the space in the first line, and the whole depth given in the second line in inches.

In furnishing the reports to the press, and in filling up the bulletin, Form 3, the daily change will be given. This change will be obtained by taking the difference between the current report and that of the preceding day.

27. Whenever any sudden or unusual change occurs in the condition of the river between the regular hours of observation, a special series of observations will be made and the observed depth will be reported in the usual manner at the next succeeding telegraphic report, and these special reports will be continued tri-daily (one at eacli telegraphic report) until the river resumes its normal condition, when the morning and midnight specials will be discontinued.

28. In carrying out these instructions, observers will use the cipher-words in the column headed "Rise," when the river is rising at the date of report, and those in the column headed "Fall," when it is falling.

29. The observations for the morning and midnight special river-reports will be made within an hour of the time of report if practicable.

Observers must exercise great care in making and recording the river-reports, in order that they can be relied upon as accurate by interested parties.

30. The amount of rain-fall (or melted snow) will be measured and reported at each of the three telegraphic reports only.

INSTRUMENTS.

31. Each station will be supplied with the following instruments:

Two standard barometers, (Green's.)

Two standard thermometers, (Green's.)

One standard hygrometer, (Glaisher's model.)

One maximum thermometer.

One minimum thermometer.

One anemometer, (Robinson's,) with self-registering attachment.

One wind-vane.

One rain-gauge.

One clock.

Other instruments may be added from time to time as the necessity for their use becomes apparent.

BAROMETER.

32. The barometers will in all cases be carefully compared with the standard at this office before issue, and the amount of instrumental error will be sent with each when it leaves this office.

The two barometers furnished each station will be carefully compared by the observer in charge once a month, making a series of comparative readings of not less than twenty in number, which will be recorded in full in the daily journal as soon as made. In making out the monthly abstract of the journal these readings will be embodied in the instrumental report; they must not be corrected for elevation, but for temperature and instrumental error only.

No change of instrumental error will be made by any observer without direct authority from this office.

The barometer should be placed in a room of a temperature as uniform as possible, not heated, nor too much exposed to the sun. It should be suspended at the height of the eye, near a window, in such a manner as to be lighted perfectly without exposure either to the direct rays of the sun or to the currents of air which are always found at the window-casings and doors. To protect the instrument from external injuries, from dust, and from the direct radiation of warm bodies or the currents of air from the window, observers will fasten the wooden case in which it is carried firmly against the wall in a vertical position near the window, in such a manner that the cover will open in a direction parallel to the panes. An opening large enough to admit the tube of the barometer will be cut in the upper end of the box; and directly above this, at the distance of one inch, a strong hook will be driven into the wall. This hook should extend two or three inches beyond the box, and upon it the instrument will be suspended. When not in use the cover will be closed; but when an observation is to be taken it will be opened, and the instrument drawn out on the hook, clear of the box, and in

the full light of the window. After the observation is made the barometer will be slipped back into the box.

33. All readings of the barometer taken for telegraphic transmission will be corrected by the observer making the observation, for instrumental error, for temperature, and for elevation, before they are sent from his station. In correcting for temperature, the reading of the attached thermometer will be used, while in correcting for elevation the temperature used will be that of the exposed or open-air thermometer.

In correcting for elevation, the height of the surface of the mercury in the cistern of the barometer above the ground must be added, in all cases, to the height of the station above sea-level, as in the following example, viz: Suppose height of station above sea-level to be 670 feet; height of mercury (surface) in cistern to be 17 feet above the ground; then the elevation to be corrected for would be 687 feet.

In correcting for temperature, Table XVII, pages 66 to 71, Paper C, of Guyot's tables, will be used; and for elevation, Table XIX, page 92, Paper D, of the same book, when special tables are not prepared under the direction of this office.

34. In transporting a barometer, even across a room, it should be screwed up and carried with its cistern uppermost. For traveling, it is provided with a wooden case. On steamboats or railroads, it should be hung up by a hook in the state-room or car, and the lower end firmly strapped to the side of the room or car to prevent jarring. In wheeled vehicles, it should be carried by hand, supported by a strap over the shoulder, or held upright between the legs; but it should not be allowed to rest on the floor of the carriage, for a sudden jolt might break the tube. If carried on horseback, it should be strapped over the shoulders of the rider, where it is not likely to be injured, unless the animal is subject to a sudden change of gait. When about to be used, it should be taken from its case, and, while screwed up, gently inverted and hung up, when it can be unscrewed. While it has its cistern uppermost, the tube is full-is one solid mass of metal and glass-and not easily injured, but when hung up a sudden jolt might send a bubble of air into the vacuum at the upper end of the tube, and the instrument would be useless until repaired. Observers must never swing the barometer or endeavor to force the mercury against the top of the tube without first screwing up the large adjusting screw at the base of the cistern.

If the cistern should become dirty, it can be cleaned with safety, and without changing, in the slightest degree, the zero of the instrument. Everything used in the operation must be clean and dry. Blowing upon any of the parts must be avoided, as the moisture from the breath is injurious.

The instrument being placed upright, the cistern uppermost, unscrew and take off the brass casing which incloses the wooden and leathern part of the cistern. This wooden part (which has the grain crosswise, and therefore is not air-tight) is made in two pieces, fastened together by four screws and four brass pieces, each in the form of a half of a circular ring. It will be necessary to take out two of these screws and loosen the other two, when the brass pieces can be taken off. The upper wooden piece, to which the bag is attached, can then be lifted off, and the mercury will be exposed. By then inclining the instrument a little, a portion of the mercury in the cistern may be poured out in a clean vessel at hand to receive it, when the end of the tube will be uncovered. This is to be closed by the gloved hand, when the instrument can be inverted, the cistern emptied, and the tube brought again to its upright position. Great care must be taken not to permit any mercury to pass out of the tube. The long screws which fasten the glass portion of the cistern to the other parts can then be taken off, the various parts wiped with a clean cloth or handkerchief, and restored to their former positions. The mercury which had been taken out of the cistern must now be cleaned, or it must be replaced by other that is clean and pure. If the old mercury is merely dusty, or dimmed by a film of oxide, the cleaning may be effected by straining it through chamois-leather, or through a funnel with a capillary hole at the end of a size to admit of the passage of but a small thread of the metal. Such a funnel is conveniently made of letter-paper. The dust will adhere to the skin or paper, and the filtered mercury will present a clean and bright appearance. At stations where muriatic acid can be procured, the mercury may be easily and quickly cleaned by mixing about two ounces of the acid with it in a small vessel or cup and then pouring into the vessel clear water until it overflows and carries off all the impurities. When sufficiently pure the water will be poured off and the mercury heated over a gas or lamp light until all remaining moisture is expelled. If chemically impure, it should be rejected, and fresh, clean mercury used. With such clean mercury the cistern should be filled as nearly full as possible, the wooden portions put together and securely fastened by the screws and clamps, the brass casing screwed on, and the screw at its end screwed up. The instrument can then be hung up and re-adjusted. The tube and its contents having been undisturbed, the instrument should read the same as before. If a little mercury has been lost during the operation, and there is none at hand to replace it, no serious harm has been done; but if much is lost, the open end of the tube may become exposed in inverting the instrument, in which case air may enter. To guard against this error, a little fresh mercury will be added.

Station barometers will not be cleaned unless ordered by this office, or by an inspecting officer, or when such action appears to be absolutely necessary by the presence of air in the tube. In any case the fact will be promptly reported to this office, stating the number of the instrument so cleaned, with date, and result of the operation.

35. Each observer upon establishing a new station will, as soon as he is furnished with the correct elevation of his barometer above sea-level, prepare a table for reducing the barometrical observations to that level, in accordance with the following formula:

Formula.

(Guyot's tables, Paper D, page 88.)

f h'
0 = X
N h

c, is the correction required; f, the elevation of the station; N, the factor from the table on page 92; h', the reading of the barometer corrected for temperature; and h, the normal height of the barometer at sea-level, which may be assumed to be 30 inches for all stations.

For all observations above 30.20 and below 29.80 the full formula will be used; but f between those numbers the first number only, c = need be used. N

36. The following-named stations having been furnished with a constant correction, are excepted from the provisions of the foregoing paragraph:

Mount Washington, N. H.

Cheyenne, Wyoming Ter.

Denver, Colo.

Santa Fe, N. Mex.
Corinne, Utah.

Virginia City, Mont.

Fort Benton, Mont.

Pike's Peak, Colo.

37. This table will be made to cover the range of the barometer from 28.80 to 30.80, and will give a correction for every five-hundredths of an inch, and the full formula given in paragraph 1 will be used in its preparation. The table must be forwarded to this office for revision and approval before it is adopted by the observer.

THERMOMETER.

38. The thermometer should be hung in the instrument-shelter in such a manner that it will be always in the shade, and at least one foot from the wall of the building to which the shelter is attached, where the Smithsonian form of shelter is used. It must be protected against the light reflected from surrounding objects, and from rain, snow, and hail. The instrument must be placed exactly perpendicular, the middle of the scale being at the height of the eye in order to prevent error in reading. The readings should be made at all times, and especially in the winter, through the panes, without opening the window, when the shelter is built out from a window. When the shelter is built upon a roof, great care must be exercised in making the readings in order to prevent the instrument from being affected by the heat of the body or of the lantern at night. The observation must be made as rapidly as is consistent with accuracy.

HYGROMETER.

39. The hygrometer will be placed in the same shelter as the thermometer, and at a distance of one foot from it. The cistern will be kept supplied with pure water at all times when the temperature of the air is above the freezing point, and the cover of the wet bulb will be changed every month, and the bulb carefully cleaned. The cover may be washed as often as necessary, without removal, by means of a jet of clean water from a small syringe.

When the temperature of the air is below the freezing point the water will be emptied from the cistern, and in making an observation the wet bulb will be moistened with cold water, and the instant the mercury has reached its minimum its height will be noted. Alcohol must not be used.

The relative humidity of the air will be obtained from Table VII, page 46, of Guyot's Tables, when special tables are not furnished from this office.

Especial care must be taken to keep the tubes of the hygrometer clean, and the wet bulb properly moistened, and to make the observations and deductions accurately, as

the humidity of the air forms an important element in all calculations of atmospheric changes.

Whenever the dry bulb of the hygrometer is observed to show a higher temperature than the exposed thermometer under similar exposure, the observer will cut a circular opening, about three inches in diameter, in the board to which the dry and wet bulbs are attached, and directly behind the bulbs.

MAXIMUM AND MINIMUM THERMOMETERS.

40, The board which accompanies these instruments will be securely fastened with screws, in a horizontal position, upon the side of the instrument-shelter, or observatory, near the hygrometer and exposed thermometer.

The brass support for the minimum will be screwed into the upper part of the board and the holes so arranged as to slightly incline the left end of the support.

The top of the thermometer will be fastened by the small brass screw upon the support, while the lower end will be dropped into the notch to the left.

For the support of the maximum thermometer the long brass pin with a nut will be screwed into the board, in the hole to the extreme right. The nut will be taken off and the pin slipped through the hole in the upper end of the instrument, which will be securely fastened by replacing the nut and securing it tightly. The plain brass pin is then inserted in the hole at the left of the board, and the thermometer placed upon it so as to incline slightly in that direction.

The end of the pin to which the maximum is attached must be occasionally oiled to prevent friction.

After unpacking the minimum it must be carefully compared with the exposed thermometer, and if an air-speck is found in the column the bulb will be immersed in warm water until all the air-bubbles disappear in the space at the top of the tube, great care being taken not to break the bulb by heating it too suddenly.

After fastening the top of the minimum upon the support, the lower end of the instrument will be raised until the top of the small index touches the top of the column of spirit.

The instrument is read by observing the number of degrees upon the scale where the top of the index rests. After taking a reading, the bulb or lower end of the thermometer, should be elevated until the index comes down to the temperature of the air, at the time of the observation, and the instrument will then be dropped into the notch at the left of the support, as before.

The maximum is read by observing the number of degrees upon the scale at the top of the column of mercury.

After taking a reading the observer will remove the pin to the left and then take hold of the thermometer, about three inches from the top, and spin it around several times, or until the top of the column is brought down to the temperature of the air at the time of observation. Care must be taken not to touch the bulb, and also that the nut is screwed up sufficiently tight to prevent the instrument from striking against the side of the board to which it is fastened. After adjustment, gradually raise the instrument to a horizontal position, and insert the pin as before.

Care should be taken in elevating the thermometer not to raise the bulb too high, as the column of mercury would then run to the upper end of the tube.

The observations upon these instruments will be made at the 11.35 p. m. report, and recorded upon Form 4, in the proper column.

ANEMOMETER.

41. The anemometer will be fixed in a vertical position upon the telescopic rod, or, when this has not been furnished, a post of sufficient height to bring the dial on a level with the eye of the observer, and must be in an exposed situation, so as to receive the full force of the wind; when possible, this post should be framed into the roof, to steady it and prevent the instrument from vibrating; but when this cannot be done, it should be framed at the bottom into two pieces of scantling, not less than three feet in length, that cross each other at right angles, and which can be nailed fast to the roof or platform upon which the instrument is placed. Short braces can be added when necessary to insure steadiness. The outer dial of the instrument is graduated in miles and tenths of miles-the figures 1, 2, 3, &c., indicating miles, and the subdivisions tenths. One complete revolution of this dial is equivalent to ten miles of wind, and carries the inner dial forward one subdivision. This inner dial registers up to 990 miles, and will not be used in making the ordinary observations, but observers will assure themselves, by making a daily comparative reading, that the record of the dials and that of the cylinder read alike at the time of changing the record-sheets on the selfregistering attachment at mid-day. When a discrepancy is found to exist between the two records, the anemometer will be carefully examined as to the condition of the