sible to select one or two which register most nearly correct. It is well to keep a permanent record of the results of each tube tested. By so doing the navigator will soon obtain valuable information as to the performance of the various tubes and the degree to which they may be trusted. Such a record should, of course, take into account the various conditions affecting the result. It will be noted that the factors which produce errors may be divided roughly into three groups:

(a) Inherent: Those which occur as a result of permanent defects in the tube, such as the variation of the bore from a true cylinder, variation in the thickness of the cap, etc.

(b) External: Those which occur as a result of the conditions under which the sounding was taken, variations of temperature or barometric pressure from the normal, etc.

(c) Accidental: Those which affect a single sounding, due to the failure of the tube to register properly, leakage of air, loss of water from leaky valve, errors due to the presence of salt in the tube, etc.

These accidental errors are probably the most serious of the three types, both because they are apt to be larger in amount and because it is impossible to foresee when they will occur. But, on the other hand, they occur only as a result of a few known causes, already enumerated, and therefore by the exercise of proper caution in the use of the tubes that they may be to a large extent eliminated. If the ordinary glass tube is used, see that the bore is thoroughly dry and free from salt and that the cap makes a tight fit. If using a sounder, see that the tube is free from water and that the valves are tight and well oiled. And, above all, during the course of the sounding take an occasional up-and-down cast as a check, for by that means alone can one be sure that the proper results are being obtained.

The smallest possible number of tubes should be used. It is obviously much better to use over and over again one tube which is giving good results than to use a number whose errors are uncertain. This is particularly desirable where sounders involving valves are used. If a tube shows no bottom at 100 fathoms, examine the arming to make sure that the lead actually failed to find bottom.

Finally, beware of overconfidence. Tubes which have been working properly for a number of soundings suddenly develop errors. It is chiefly for this reason that they have been discarded for surveying operations. Assuming that the accidental errors can be reasonably controlled, the inherent and external errors present no serious difficulty.

As already indicated, the bore of a tube (or at least of any tube which is capable of constant use) can be tested with mercury, and those tubes rejected which show variations in bore greater than about 5 per cent. Errors due to variations in the thickness of caps can be eliminated by using a scale graduated for a true length of 24 inches (the length of the glass tube) and removing the cap before the sounding is read. Errors due to differences between air and water temperatures can be reduced to a minimum which can usually be neglected by immersing the tube before using in a bucket of sea water newly drawn, so that its temperature has not had time to change. Care should, of course, be taken to see that no water enters the tube. When this is done there may still remain an error due to the difference in temperature of the water at the surface and at the bottom. This may, if desired, be corrected by sending down a self-registering thermometer with the lead, but for the ordinary purposes of navigation this is a refinement which may be ignored. There is no ready method available for correcting the error due to variations in the barometric pressure. The correction should be applied to the sounding recorded.

BOUNDARY LINES OF THE HIGH SEAS

The following lines divide the high seas from rivers, harbors, and inland waters described in this volume. Waters inshore of the lines here laid down are "inland waters," and upon them the pilot rules for western rivers (where noted) or the inland rules and pilot rules given on page 217 apply. Upon the high seas, viz, waters outside of the lines here laid down, the international rules given on page 210 apply.

FLORIDA REEFS AND KEYS.-A line drawn from the easterly end of the northerly jetty at the entrance to the dredged channel one-half mile northerly of Norris Cut, 94° (E. 4 S.), 15% miles, to Florida Reefs North End Whistling Buoy,

W (HS); thence 178° (S. 4 E.), 8 miles, to Biscayne Bay Sea Bell Buoy, 1; thence 182° (S. % W.), 2% miles, to Fowey Rocks Lighthonse; thence 188° (S. % W.), 64 miles, to Triumph Reef Beacon, O; thence 193° (S. by W.), 42 miles, to Ajax Reef Beacon, M; thence 194° (S. by W. % W.), 2 m'les, to Pacific Reef Beacon, L; thence 1962° (S. by W. % W.), 5 miles, to Turtle Harbor Sea Buoy, 2; thence 210° (SSW. 2 W.), 4% miles, to Carysfort Reef Lighthouse; thence 2092° (SSW. 2 W.), 54 miles, to Elbow Reef Beacon, J; thence 2172° (SW. 4 S.), 94 miles, to Molasses Reef Gas Buoy, 2 M; thence 2352° (SW. 4 W.), 6 miles to Conch Reef Beacon, E; thence 2342° (SW. 4 W.), through Crocker Reef Beacon, D, 10% miles, to Alligator Reef Lighthouse; thence 234° (SW. % W.), 10% miles, to Tennessee Reef Buoy, 4; thence 251° (WSW. % W.), 101⁄2 miles, to Coffins Patches Beacon, C; thence 247° (SW. by W. 4 W.), 84 miles, to Sombrero Key Lighthouse; thence 2531⁄2° (WSW. % W.), 164 miles, to Looe Key Beacon, 6; thence 2572° (WSW. 4 W.), 6% miles, to American Shoal Lighthouse; thence 2532° (WSW. % W.), 2% miles, to Maryland Shoal Beacon, S; thence 259° (WSW. % W.), 54 miles, to Eastern Sambo Beacon, A; thence 253° (WSW. 4 W.), 24 miles, to Western Sambo Beacon, R; thence 257° (WSW. 5% W.), through Western Sambo Buoy, 2, 51⁄2 miles, to Key West Entrance Gas Buoy (PS); thence 262° (W. % S.), 44 miles, to Sand Key Lighthouse; thence 261° (W. by S.), 24 miles, to Western Dry Rocks Beacon, 2; thence 268° (W. % S.), 31⁄2 miles, through Satan Shoal Buoy (HS) to Vestal Shoal Buoy, 1; thence 2742° (W. % N.), 54 miles, to Coal Bin Rock Buoy, CB (HS); thence 3242° (NW. 5% N.), 74 miles, to Marquesas Keys left tangent; from northwesterly point Marquesas Keys 59° (NE. by E.), 4% miles, to Bar Buoy, 1, Boca Grande Channel; thence 83° (E. % N.), 94 miles, to Northwest Channel Entrance Bell Buoy, 1, Northwest Channel into Key West; thence 68° (NE. by E. % E.), 231⁄2 miles, to northerly side of Content Keys; thence 49° (NE. 1⁄4 E.), 29 miles, to East Cape, Cape Sable.

CHARLOTTE HARBOR AND PUNTA GORDA, FLA.--Eastward of Charlotte Harbor Entrance Gas and Bell Buoy (PS), off Boca Grande, and in Charlotte Harbor, in Pine Island Sound and Matlacha Pass. Pilot Rules for Western Rivers apply in Peace and Miakka Rivers north of a 250° and 70° (WSW. and ENE.) line through Mangrove Point Light; and in Caloosahatchee River northward of the steamboat wharf at Punta Rasa.

TAMPA BAY AND TRIBUTARIES, FLA.-From the southerly end of Long Key 245° (SW. by W. 5% W.) 9 miles, to Tampa Bay Gas and Whistling Buoy (PS); thence 129° (SE. 4 E.), 61⁄2 miles, to Bar Bell Buoy (PS), at the entrance to Southwest Channel; thence 103° (E. by S.), 24 miles, to the house on the north end of Anna Maria Key. Pilot Rules for Western Rivers apply in Manatee River inside Manatee River Entrance Buoy, 2; in Hillsboro Bay and River inside Hillsboro Bay Light, 2.

ST. GEORGE SOUND, APALACHICOLA BAY, CARRABELLE AND APALACHICOLA RIVERS, AND ST. VINCENT SOUND, FLA.--North of a line from Lighthouse Point 246° (SW. by W. 5% W.), 134 miles, to southeasterly side of Dog Island; to northward of East Pass Bell Buoy, 1, at the entrance to East Pass, and inside West Pass Bell Buoy (PS) at the seaward entrance to West Pass. Pilot Rules for Western Rivers apply in Carrabelle River inside the entrance to the dredged channel; in Apalachicola River northward of Apalachicola Dredged Channel Entrance Buoy, 2.

PENSACOLA HARBOR.--From Caucus Cut Entrance Gas and Whistling Buoy, 1A, 3° (N. 1 W.), tangent to easterly side of Fort Pickens, to the shore of Santa Rosa Island, and from the buoy northward in the buoyed channel through Caucus Shoal.

MOBILE HARBOR AND BAY.-From Mobile Entrance Gas and Whistling Buoy (PS) 40° (NE. % N.) to shore of Mobile Point, and from the buoy 320° (NW.) to the shore of Dauphin Island. Pilot Rules for Western Rivers apply in Mobile River above Choctaw Point.

SOUNDS, LAKES, AND HARBORS ON THE COASTS OF ALABAMA, MISSISSIPPI, and LOUISIANA, BETWEEN MOBILE BAY ENTRANCE AND THE DELTA OF THE MISSISSIPPI RIVER. From Sand Island Lighthouse 259° (WSW. 5% W.), 432 miles to Chandeleur Lighthouse; westward of Chandeleur and Errol Islands, and west of a line drawn from the southwesterly point of Errol Island 182° (S. 1⁄4 E.), 23 miles, to Pass a Loutre Lighthouse. Pilot Rules for Western Rivers apply in Pascagoula River, and in the dredged cut at the entrance to the river, above Pascagoula River Entrance Light, A, marking the entrance to the dredged cut.

NEW ORLEANS HARBOR AND THE DELTA OF THE MISSISSIPPI RIVER.-Inshore of a line drawn from the outermost mud lump showing above low water at the entrance to Pass a Loutre to a similar lump off the entrance to Northeast Pass; thence to a similar lump off the entrance to Southeast Pass; thence to the outermost aid to navigation off the entrance to South Pass; thence to the outermost aid to navigation off the entrance to Southwest Pass; thence northerly, about 191⁄2 miles, to the westerly point of the entrance to Bay Jaque.

SABINE PASS, TEX.-Pilot Rules for Western Rivers apply to Sabine Pass northward of Sabine Pass Gas and Whistling Buoy (PS), and in Sabine Lake and its tributaries. Outside of this buoy the International Rules apply.

GALVESTON HARBOR.-A line drawn from Galveston North Jetty Light 129° (SE. by E. 4 E.), 2 miles, to Galveston Bar Gas and Whistling Buoy (PS); thence 276° (W. % S.), 24 miles, to Galveston (S.) Jetty Lighthouse.

BRAZOS RIVER, TEX.-Pilot Rules for Western Rivers apply in the entrance and river inside of Brazos River Entrance Gas and Whistling Buoy (PS). International Rules apply outside the buoy.

GENERAL RULE.-At all buoyed entrances from seaward to bays, sounds, rivers, or other estuaries for which specific lines have not been described, Inland Rules shall apply inshore of a line approximately parallel with the general trend of the shore, drawn through the outermost buoy or other aid to navigation of any system of aids.

RULES OF THE ROAD INTERNATIONAL RULES TO PREVENT COLLISIONS OF VESSEL

Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That the following regulations for preventing collisions at sea shall be followed by all public and private vessels of the United States upon the high seas in all waters connected therewith navigable by seagoing vessels.

ART. 30. Nothing in these rules shall interfere with the operation of a special rule, duly made by local authority, relative to the navigation of any harbor, river, or inland waters.

PRELIMINARY

In the following rules every steam vessel which is under sail and not under steam is to be considered a sailing vessel, and every vessel under steam, whether under sail or not, is to be considered a steam vessel.

The words "steam vessel" shall include any vessel propelled by machinery. A vessel is "under way," within the meaning of these rules, when she is not at anchor, or made fast to the shore, or aground.

RULES CONCERNING LIGHTS AND SO FORTH

The word "visible" in these rules when applied to lights shall mean visible on a dark night with a clear atmosphere.

ARTICLE 1. The rules concerning lights shall be complied with in all weathers from sunset to sunrise, and during such time no other lights which may be mistaken for the prescribed lights shall be exhibited.

ART. 2. A steam vessel when under way shall carry-(a) On or in front of the foremast, or if a vessel without a foremast, then in the fore part of the vessel, at a height above the hull of not less than twenty feet, and if the breadth of the vessel exceeds twenty feet, then at a height above the hull not less than such breadth, so, however, that the light need not be carried at a greater height above the hull than forty feet, a bright white light, so constructed as to show an unbroken light over an arc of the horizon of twenty points of the compass, so fixed as to throw the light ten points on each side of the vessel, namely, from right ahead to two points abaft the beam on either side, and of such a character as to be visible at a distance of at least five miles.

(b) On the starboard side a green light so constructed as to show an unbroken light over an arc of the horizon of ten points of the compass, so fixed as to throw the light from right ahead to two points abaft the beam on the starboard side, and of such a character as to be visible at a distance of at least two miles.

(c) On the port side a red light so constructed as to show an unbroken light over an arc of the horizon of ten points of the compass, so fixed as to throw

the light from right ahead to two points abaft the beam on the port side, and of such a character as to be visible at a distance of at least two miles.

(d) The said green and red side lights shall be fitted with inboard screens projecting at least three feet forward from the light, so as to prevent these lights from being seen across the bow.

(e) A steam vessel when under way may carry an additional white light similar in construction to the light mentioned in subdivision (a). These two lights shall be so placed in line with the keel that one shall be at least fifteen feet higher than the other, and in such a position with reference to each other that the lower light shall be forward of the upper one. The vertical distance between these lights shall be less than the horizontal distance.

ART. 3. A steam vessel when towing another vessel shall, in addition to her side lights, carry two bright white lights in a vertical line one over the other, not less than six feet apart, and when towing more than one vessel shall carry an additional bright white light six feet above or below such lights, if the length of the tow measuring from the stern of the towing vessel to the stern of the last vessel towed exceeds six hundred feet. Each of these lights shall be of the same construction and character, and shall be carried in the same position as the white light mentioned in article two (a), excepting the additional light, which may be carried at a height of not less than fourteen feet above the hull.

Such steam vessel may carry a small white light abaft the funnel or aftermast for the vessel towed to steer by, but such light shall not be visible forward of the beam.

ART. 4. (a) A vessel which from any accident is not under command shall carry at the same height as a white light mentioned in article two (a), where they can best be seen, and if a steam vessel in lieu of that light two red lights, in a vertical line one over the other, not less than six feet apart, and of such a character as to be visible all around the horizon at a distance of at least two miles; and shall by day carry in a vertical line one over the other, not less than six feet apart, where they can best be seen, two black balls or shapes, each two feet in diameter.

(b) A vessel employed in laying or in picking up a telegraph cable shall carry in the same position as the white light mentioned in article two (a), and if a steam vessel in lieu of that light three lights in a vertical line one over the other not less than six feet apart. The highest and lowest of these lights shall be red, and the middle light shall be white, and they shall be of such a character as to be visible all around the horizon at a distance of at least two miles. By day she shall carry in a vertical line, one over the other, not less than six feet apart, where they can best be seen, three shapes not less than two feet in diameter, of which the highest and lowest shall be globular in shape and red in color, and the middle one diamond in shape and white.

(c) The vessels referred to in this article, when not making way through the water shall not carry the side lights, but when making way shall carry them.

(d) The lights and shapes required to be shown by this article are to be taken by other vessels as signals that the vessel showing them is not under command and can not therefore get out of the way.

These signals are not signals of vessels in distress and requiring assistance. Such signals are contained in article thirty-one.

ART. 5. A sailing vessel under way and any vessel being towed shall carry the same lights as are prescribed by article two for a steam vessel under way with the exception of the white lights mentioned therein, which they shall never carry.

ART. 6. Whenever, as in the case of small vessels under way during bad weather, the green and red side lights can not be fixed, these lights shall be kept at hand, lighted and ready for use; and shall, on the approach of or to other vessels, be exhibited on their respective sides in sufficient time to prevent collision, in such manner as to make them most visible, and so that the green light shall not be seen on the port side nor the red light on the starboard side, nor, if practicable, more than two points abaft the beam on their respective sides. To make the use of these portable lights more certain and easy the lanterns containing them shall each be painted outside with the color of the light they respectively contain, and shall be provided with proper screens.

ART. 7. Steam vessels of less than forty. and vessels under oars or sails of less than twenty tons gross tonnage, respectively, and rowing boats, when under way, shall not be required to carry the lights mentioned in article two (a), (b),

and (c), but if they do not carry them they shall be provided with the following lights:

First. Steam vessels of less than forty tons shall carry

(a) In the fore part of the vessel, or on or in front of the funnel, where it can best be seen, and at a height above the gunwale of not less than nine feet, a bright white light constructed and fixed as prescribed in article two (a), and of such a character as to be visible at a distance of at least two miles.

(b) Green and red side lights constructed and fixed as prescribed in article two (b) and (c), and of such a character as to be visible at a distance of at least one mile, or a combined lantern showing a green light and a red light from right ahead to two points abaft the beam on their respective sides. Such lanterns shall be carried not less than three feet below the white light. Second. Small steamboats, such as are carried by seagoing vessels, may carry the white light at a less height than nine feet above the gunwale, but it shall be carried above the combined lantern mentioned in subdivision one (b).

Third. Vessels under oars or sails of less than twenty tons shall have ready at hand a lantern with a green glass on one side and a red glass on the other, which, on the approach of or to other vessels, shall be exhibited in sufficient time to prevent collision, so that the green light shall not be seen on the port side nor the red light on the starboard side.

Fourth. Rowing boats, whether under oars or sail, shall have ready at hand a lantern showing a white light which shall be temporarily exhibited in sufficient time to prevent collision.

The vessels referred to in this article shall not be obliged to carry the lights prescribed by article four (a) and article eleven, last paragraph.

ART. 8. Pilot vessels when engaged on their station on pilotage duty shall not show the lights required for other vessels, but shall carry a white light at the masthead, visible all around the horizon, and shall also exhibit a flareup light or flare-up lights at short intervals, which shall never exceed fifteen minutes.

On the near approach of or to other vessels they shall have their side lights lighted ready for use, and shall flash or show them at short intervals, to indicate the direction in which they are heading, but the green light shall not be shown on the port side nor the red light on the starboard side.

A pilot vessel of such a class as to be obliged to go alongside of a vessel to put a pilot on board may show the white light instead of carrying it at the masthead, and may, instead of the colored lights above mentioned, have at hand, ready for use, a lantern with green glass on the one side and red glass on the other, to be used as prescribed above.

Pilot vessels when not engaged on their station on pilotage duty shall carry lights similar to those of other vessels of their tonnage.

A steam pilot vessel, when engaged on her station on pilotage duty and in waters of the United States, and not at anchor, shall, in addition to the lights required for all pilot boats, carry at a distance of eight feet below her white masthead light a red light, visible all around the horizon and of such a character as to be visible on a dark night with a clear atmosphere at a distance of at least two miles, and also the colored side lights required to be carried by vessels when under way.

When engaged on her station on pilotage duty and in waters of the United States, and at anchor, she shall carry in addition to the lights required for all pilot boats the red light above mentioned, but not the colored side lights. When not engaged on her station on pilotage duty, she shall carry the same lights as other steam vessels.

ART. 9. Fishing vessels and fishing boats, when under way and when not required by this article to carry or show the lights hereinafter specified, shall carry or show the lights prescribed for vessels of their tonnage under way.

(a) Open boats, by which is to be understood boats not protected from the entry of sea water by means of a continuous deck, when engaged in any fishing at night, with outlying tackle extending not more than one hundred and fifty feet horizontally from the boat into the seaway, shall carry one all-round white light.

Open boats, when fishing at night, with outlying tackle extending more than one hundred and fifty feet horizontally from the boat into the seaway, shall carry one all-round white light, and in addition, on approaching or being approached by other vessels, shall show a second white light at least three feet below the first light and at horizontal distance of at least five feet away from it in the direction in which the outlying tackle is attached.