been studied for about two hundred years, for Le Blond de la Tour, the French engineer, built the first levee, a mile long, in front of the infant city of New Orleans in 1717. Now there are close to 300,000,000 cubic yards of them, and except where the mouths of tributaries or natural elevations preclude their necessity they extend on both sides of the stream from Cape Girardeau, Mo., to the Gulf, 1,039 miles.

Sixteen feet is a good average height, with an eight-foot crown, and a fortyeight foot base. The proportion of three to one is kept, so that the Morganza La.,-levee, the greatest dike in the world outside of Holland, is thirty-five feet high and more than one hundred feet wide at the base-a mountain range in miniature.

Of course, a levee has to be built from the dirt readily at hand, SO there are "buckshot" loam levees, Louisiana mud levees, and sandy levees, ranking in value in the order named. "Buckshot" is

the material par excellence. It is tough; it packs well; it offers resistance

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to seepage; does not cave away, or suffer much from wave wash-but "buckshot" is not to be found everywhere.

One rule is invariable. Rock must not be used. Not a stone or a stick goes into a levee. These tend to make a levee porous, and a vertical filter is the last thing desired. Packed earth is the best, and for this reason, an old levee is better than a new. The earth packs and dries harder and harder with each succeeding summer, and grows a thick matting of sod, than which there is no better protection from wave wash. Every effort is made to grow grass on the levees.

Where a wide batture can be found, the situation is even more safe. The batture is the flat table of land which stretches out to the channel of the river, a flat stretch between the toe of the levee and the stream in low water. A batture is a silt deposit, but so old, often, that goodsized oaks and thick screens of willows grow upon it. The reason for the factor of safety a batture offers is almost self-evident. The current over the batture seldom is as swift as in mid

channel,

harm, or more, than the crawfish. Both these pests attack the levee from the river side, boring into the earth, straight through, perhaps, or maybe tortuously. These holes spurt water when the river reaches the level of their openings, and if allowed to flow unchecked, will increase in size until they undermine the entire embankment, and a crevasse results.

They are fought in the same manner. If discovered before high water, the holes are repaired then. If they are not discovered until the flood is on, a box is built out into the river in front of the levee, the embankment forming the inner side. This box is filled with dirt sacks. This stops the leak, but it is expensive, since the box must be large enough to be sure to enclose the intake, which naturally cannot be seen or found beneath the water.

Seepage is one of the first troubles encountered when the river begins to rise. Through the forty, sixty or hundred foot base, the water will seep, and

up from beneath as well. Ditches are the remedy for this. Some seepage seems inevitable. Unless it becomes so heavy that it collects behind the levee and threatens to soften it, it does not mean much. If the seepage becomes serious, "blanketing" is resorted to. The "blanket" is of dirt, spread over the face of the levee, plastering it thick with mud which works its way into the crevices which are leaking.

Day and night the levees are guarded, when the river threatens thus, militiamen and volunteers do turn about with Winchesters and shotguns, watching for any sign of trouble. There is another reason for the guards. A break on one side of the river relieves the danger for miles on the other side above and below. To save his own broad acres, temptation to use a little dynamite across the river might be too strong for some weak brother. So the rifles mean business, and when one visits a levee in flood time, it is with adequate explanation of one's

reasons.

A

REPETITION

never once failing to record the presence of ice.

The instrument is really an adaptation of the electrical resistance thermometer. It is permanently attached to the prow of the vessel, and is connected by electrical wires. to a dial in the chart room, where every slight variation in the temperature of the water may now be recorded. Professor Barnes says that at present navigators rely almost entirely on the lookout to detect the presence of ice, and the danger of this practice has been emphasized by the Titanic disaster.

tion of the Titanic is now declared to be impossible, provided a recently invented instrument be installed, and its indicator faithfully observed on all ocean lines. Professor Howard T. Barnes, D. Sc., F. R. C. S., director of the physical laboratories at McGill University, Montreal, is the inventor of this instrument, which is attracting much attention among scientific men both on this continent and in Great Britain. He calls his invention the micro-thermometer. It is, in reality, a super-sensitive thermometer which, it is claimed, will infallibly detect an iceberg at a distance of two miles on the windward side, and seven miles on the leeward side. Professor Barnes has conducted numerous experiments with the instrument on the Canadian government vessels in the river and gulf of the St. Lawrence, and these have in every way borne out his claims. In May of this year, when on his way to England, to lecture on his invention, by invitation, before the Royal Institute, he conducted experiments on the Canadian Northern liner, Royal George, sailing from Halifax to Liverpool. This was soon after the Titanic disaster, when ice was still plentiful along the steamship tracks on the Atlantic, and again the instrument fully established the assertions of its inventor,

"A show is also made," he said, "of taking the temperature of the water, but the method of doing this is so crude that

little reliance is placed upon it by navigators. Captain Lecky, in his 'Wrinkles on Navigation,' shows this conclusively. The method now in use is to pull a bucket of water up over the side of the vessel, and to dip a mercury or alcohol thermometer in it to get a record of the temperature. perature. It is just an ordinary house thermometer that is used. It is a haphazard and unscientific method of taking observations of sea temperaturefirst, because records are only obtained at more or less long intervals; second, because it is impossible by this means to detect small variations, while variations of half a degree, or even a whole degree, are apt to go unnoticed.

"Now the micro-thermometer is so sensitive that it will record a variation of

WIND DIRECTION:

THE ICEBERG

one-thousandth of a degree, and so striking is its record that whereas on an ordinary thermometer a single degree is usually represented by only one-eighth of an inch, the micro-thermometer represents a single degree by an interval of two feet.

"Moreover, the micro-thermometer is designed, not to be dipped into buckets of water at frequent intervals, but to be permanently attached to the ship under the water line, and, by means of wires leading from it to the chart room, to make a continuous record in the chart room of the water temperature. With this thermometer being towed along with the ship, and with a continuously-recording instrument attached to it in the chart room, the presence of an iceberg unerringly makes itself known by the persistence of a gradient of temperature.

"Here is how I would equip a ship. An iceberg, of course, is continuously giving off a current of cold water all around it. This cold water, being fresh

water, is lighter than the salt water, and spreads out over the surface of the sea for two miles on the windward side, and seven miles on the leeward side. Now if a micro-thermometer were fitted at the bow, about two feet below the water line, and another micro-thermometer at the stern, as deep down as the draught of the ship would allow, the bow thermometer would catch the cold surface current, while the stern thermometer would remain at the normal sea temperature. In this way whenever the differential record read so that the bow thermometer was colder than the deep stern instrument, this would be taken as an indication of disturbance due to the presence of icean unmistakable indication, because it could be due to no other cause. If the recording instrument showed this temperature to persist and become greater, the ship would be approaching the ice; if it decreased the ship would be leaving the ice behind."