dial-pegs, or contact-pins, (which should always be perfectly straight,) and the contact-springs. The latter are liable to become corroded by the action of the electric spark or moisture, and must be kept clean.

42. To obtain the velocity of the wind for the regular observations when the selfregistering attachment is out of order, two readings of the outer dial must be taken, with an interval of five minutes between them, and the difference between these readings will be the distance in tenths of miles traveled by the wind in that interval. This, multiplied by twelve and divided by ten, will give the proximate velocity, in miles per hour. Example: suppose the index of the outer dial to be at 3 when the first reading is taken, and at 3.6 five minutes after, the difference, 6, is the distance traveled in that time; and this, multiplied by twelve and divided by ten, gives a velocity of seven and two-tenths miles per hour. Whole numbers only will be used in expressing the velocity. When the decimal is greater than five-tenths, the unit's figure will be increased i one; when five or less it will be thrown out. The whole distance traveled by the wind in any twenty-four hours, provided it does not exceed one thousand miles, may be obtained from the inner dial by a double observation, making the interval twenty-four hours instead of five minutes, and reading the result directly from the dial, without calculation as above described for observations from the outer dial, and will be entered on both copies of Form 4.

43. The following directions for setting up and the general management of the electric self-recording anemometer attachment adopted by this office will be observed at all stations supplied with the apparatus.

Near the top of the post on which the anemometer is fixed, place two screws, "c". and "d," (Fig. 1,) to each of these screws fasten the wires separately, (the insulated wire to one, and the naked wire to the other,) leaving just sufficient of the upper end of each wire to reach to the outside ends of the contact-bars "a" and "b," to which securely fasten with the binding screws, taking great care not to loosen the insulating attachment "g." Then pass the lower ends of the wire down the post, over the roof, and down the side of the house (securing so the wind will not sway them) to the top of the office-window, pass them in through two small holes (where the sash and shutters will not injure them) and down the inside. In crossing the roof it is well to fasten them between two wooden strips, one on top of the other. One wire should then go to the screw-cup "h" (Fig. II) and the other to one pole of the battery at "i," then from the other pole, "m," of the battery run a wire to the screw-cup "k," when the circuit is completed and the armature will be closed once for each mile the wind travels.

Particular care must be taken that all of the connections are tight.

For putting on the paper-Place the cylinder "s" on a table in front, with the screw "r" to the left hand, place the paper on the cylinder with the top of it from the screw. Let the line marked 12 m. (noon) come on the line marked on the cylinder, and place a small rubber-band on each end. The lines on each end of the paper will then exactly coincide.

Place the cylinder "s" in its position, so that the end on which there is no screw "t" will be close up to the post on which it rests. Slide the small sliding bar "n" on the horizontal bars "o" "o," until it fits on the ends of the screw axle "r;" then revolve the cylinder until the pencil rests on the end of the upper line marked 12 m., and tighten the thumb-screw "n."

To regulate the length of the mark, first move the armature set-screw "p" until the point of the pencil rests on the upper line marked 12 m., then (after loosening the setscrew which holds down the coils) move the magnet by means of the set-screw "q" until the pencil-mark is a little less than one-eighth of an inch long. The mark should never exceed one-eighth of an inch.

Care must be taken in adjusting the armature spring, so that it will not be too strong for the magnet, and still strong enough to draw back the pencil in a straight line.

The pencils should be kept pointed enough to give a clear, distinct mark.
The clock should be wound every day when the record is changed.

The record should be changed daily at 12 o'clock, noon.

At stations furnished with this self-recording apparatus, the hourly velocity of the wind will be deduced from the record of the 15 minutes (multiplied by four) immediately preceding the time of observation.

The screw posts, or, in the old style of anemometer, the connecting-bars, must be kept bright where they form connection with the conducting wires, to prevent resistance to the passage of the current.

Especial attention will be given to the large dial-screw, and when found loosened it will at once be tightened, but care must be taken that it is not screwed up tight enough to interfere with the free motion of the dials.

The anemometer will be kept well oiled, so that there will be no friction and conse. quent wear of the wheel-works.

The instrument must not be taken apart unnecessarily, and those having the new style of contacts will be manipulated with especial care.

Observers will familiarize themselves with the construction of the several parts of the anemometer, in order that they may be able to locate faults whenever the instrument is out of order.

BATTERY FOR ANEMOMETER.

44. The field-battery in use at the various stations of observation differs slightly from the ordinary form of Daniells' battery used on telegraph lines, in the manner of construction, the glass jar of the latter being dispensed with, and the negative (copper) element used as the containing vessel instead. The following directions for setting up and using this form of battery will be observed:

1. In putting the battery together for use, place the porous cup inside the copper vessel, and the star-shaped zinc element inside the porous cup.

2. Fill the copper vessel with a strong solution of sulphate of copper (preparing this liquid in another vessel by dissolving about half a pound of crystals of the sulphate in a quart of pure water) to within one inch of the top: crystals of the sulphate must never be plunged in the copper vessel, neither must sulphuric acid be used to strengthen the battery, as by so doing the copper vessel will be rapidly destroyed. The porous cup is also filled with pure water to within one inch of its top.

3. After all the cells are filled in this manner, connect the copper (positive) pole of one cup with the zinc (negative) pole of the next one by short pieces of insulated copper wire, using the copper clamps for attaching the ends of the wires to the zincs, and the fixed binding-screws for attaching them to the coppers. The main wires through which the circuit is formed will be attached to the copper and zinc elements of the outside or end cups, respectively.

4. A battery carefully put up in this manner should work with but slight diminution of force, for at least fourteen days, at the end of which time the porous cups will be taken out, emptied, washed thoroughly, and all pure copper on their outer sides removed, and will then be refilled with pure water. Care must be taken to avoid disturbing the paraffine at the bottom of the cups, as it is used there to prevent contact between the zinc and copper elements. The zincs will also be thoroughly cleaned by means of the battery-brush provided for that purpose. When properly cleaned they should present a comparatively bright surface.

5. The liquid in the copper vessels will not be changed as often as the water in the porous cups, but only when it loses its dark-blue color. It will be stirred daily, in order to keep it of equal strength above and below, as the sulphate held in solution has a tendency to settle to the bottom on account of its greater specific gravity, and thereby localizing its action.

6. The binding-screws and the ends of the small connecting wires must be kept scrupulously clean to insure good connections, and the copper vessels kept at least one inch apart to prevent contact. The cells should rest on a painted wooden base to insulate them from each other and from the earth, and care must be taken to prevent any escape of liquid from the several cells by which a connection might be formed between them.

7. Whenever practicable, observers will purchase their supply of sulphate of copper at the station where it is to be used; where this cannot be done, it will be furnished from this office.

8. The copper vessels will be kept properly painted on the outside.

45. DIRECTIONS FOR GIBBON'S ELECTRICAL RECORDING ANEMOMETER AND ANEMOSCOPE.

Setting up anemoscope.

1st. From the top of the large wind-vane remove the weather-cap, which is just above the friction-rollers.

2d. Immediately beneath the friction-rollers, and close up under the circular plate upon which the rollers run, place the bisected wooden ring a a, Fig. A, and a' a', Fig. -, on which are fastened four pieces of brass h and h', each one-eighth of the circumference of the ring.

3d. Fasten this ring by means of the iron clamp b and screw c. If necessary a band of metal, leather, or rubber must be placed inside to make the clamp fit.

4th. This ring with one of the one-eighth brass sections h must be placed so that one of the sections must be directly opposite the north, and so the opposite halves of the ring exactly meet.

5th. At the point where the arm de, which holds the friction contact f, is placed, file the upright shaft m, which holds the vane, until it is bright.