All vessels registered in Canada of not more than 250 tons registered tonnage navigating the St. Lawrence River.

Further exemptions are vessels employed in trading between any one or more of the provinces of Quebec, New Brunswick, Nova Scotia, or Prince Edward Island, and any other or others of them.

Vessels employed in voyages between any port or ports in the said Provinces or any of them and the port of New York or any port of the United States of America on the Atlantic north of New York.

Vessels employed in voyages between any port in any of the Provinces above mentioned and any port in Newfoundland.

Buoyage system.-The Canadian and United States Governments adopt, in the essential features, the same system of buoyage.

In proceeding up the St. Lawrence, or into the harbors of either country, the buoys on the starboard hand are painted red and, when numbered, have even numbers. Those on the port hand are painted black, and marked with odd numbers.

Buoys marking middle grounds are painted with black and red horizontal bands, and are passed on either hand. Those painted with black and white vertical stripes are placed in mid channel, and must be passed close-to to avoid dangers.

All starboard hand spar buoys, maintained by the Government of the Dominion of Canada, have pointed tops; and all port hand spar buoys have flat tops.

Perches, with balls, cages, etc., when placed on buoys, indicate turning points, the color and number of the buoy showing on which side they should be left.

Canadian buoys in the St. Lawrence River above Quebec are numbered on the charts under letters of the district, thus: Q, Quebec; C, Champlain; L, lake, including lake St. Peter; M, Montreal, etc. All but the plain spar buoys have their numbers and letters painted on them.

Different channels in the same bay, river, or harbor will be marked, as far as practicable, by different descriptions of buoys. Principal channels will be marked by nun buoys; secondary channels by can buoys, and minor channels by spar buoys. When there is but one channel, nun buoys, properly colored and numbered, are usually placed on the starboard side, and can buoys on the port side of it.

Day beacons, stakes, and spindles (except such as are on the sides of the channels, which will be colored like buoys) are constructed and distinguished with special reference to each locality, and particularly in regard to the background upon which they are projected.

Numbering of light vessels.-The Canadian Government, for office convenience, paints numbers on all its light vessels.

Barometer readings.-The graduation of barometric scales in millibars having been largely introduced, the following scale will prove useful in converting inches into millibars, and the reverse:

The Great Lakes are the common passage ground of North American storms, the majority of which have their origin in Bering Sea, and make their way across the entire continent. The violent storms which pass up the Atlantic coast of the United States exercise but little influence over the Lake region.

While mariners upon the Great Lakes have their best safeguard in closely observing the storm warnings issued by the Weather Service of the United States, and of the Dominion of Canada, there are many cases where a knowledge of the nature of the storms which visit the Lakes, and of the laws governing them, would prove of value. It requires but a brief period of systematic observations with the barometer and thermometer to enable the master of a vessel to keep himself fully informed, at all times, of the approach of any atmospheric disturbance likely to endanger the vessel.

The custom upon the Lakes of loading steamers until they can barely pass over the sills, and the unwieldy size of the tows carried by the fowboats, put both classes of vessels at the mercy of the wind and waves. In the first case, when overtaken by a storm, the heavily laden steamer, too deep in the water for proper handling, has simply to depend for safety upon her staunchness; in the second, the only possible resource is to cut adrift the tow, if it has not already gone to pieces. Under such circumstances, any means of predicting a coming storm, of foretelling the shifts of the wind, and the probability of a certain shore furnishing a continuous lee for anchorage has a double value. Many Lake vessels are equipped with aneroid barometers and thermometers, and it requires but a brief period of observation with these two instruments to enable the mariner to keep himself informed at all times of the approach of any extensive atmospheric disturbance likely to endanger his vessel. The United States Hydrographic Office is desirous of assisting Lake navigators in this matter, and accordingly here presents a brief description of storms in general, and the value of the barometer in predicting them.

In order to use the barometer intelligently, as a means of forecasting the weather for any region, it is necessary to have a knowl

24

BAROMETER AND LAW OF STORMS.

edge of the mean, or average, barometric pressure prevailing over the region. In consequence of their elevation above sea level, the normal barometric pressure over the Great Lakes is far below the pressure at the seacoast, actual barometric readings upon the upper lakes ranging between 28.30 inches and 30.20 inches. The elevation of each lake, the average barometric pressure over that lake, and the correction which must be added to that pressure in order to reduce it to sea level, which is the common plane of referis as follows:

ence,

For this reason the words "fair," "change," "stormy," etc., upon the face of the aneroid barometer are worse than useless when the barometer happens to be used in the Lake regions, or, indeed, at any point whose elevation differs much from sea level. The pressures given upon the United States Weather Bureau map have all been reduced to sea level by the application of the proper correction, and other observations must be similarly reduced before any comparison is possible.

The figures of the table give the average reading of a standard barometer at the temperature of freezing and placed at the level of the lake. Before comparing the reading of the vessel's barometer with them, the latter must be reduced to the same condition by the application of certain corrections, viz:

1. The initial correction.

2. The temperature correction (applied only when the barometer is mercurial).

3. The correction for height above sea level.

The initial correction is best obtained by directly comparing the barometer with some standard. The method adopted at seaports of comparing the 8 a. m. barometer readings of the vessel and Weather Bureau is inapplicable upon the Lakes, as it involves the reduction to sea level.

The temperature correction, which depends upon the reading of the attached thermometer, is required for mercurial barometers only, and may be taken from the following table:

The correction for height above lake level amounts to 0.01 inch for each 10 feet that the barometer is above the level of the lake and must be added to the barometer reading.

As an example of the application of these corrections, let the reading of a mercurial barometer, hanging 22 feet above the level of the lake, be 29.35 inches, the attached thermometer showing a temperature of 71°. Suppose that a previous comparison with a standard has shown that the barometer reads 0.13 inch too high. Then we have:

Had the barometer been an aneroid, no correction for temperature would have been required. Having applied these corrections to the barometer as read, the corrected value may be compared with the average pressure and predictions made as to the weather expected. Fine weather with a barometer below the average may occasionally occur, but only as a prelude to wind and rain.

A falling barometer, accompanied by a rising thermometer, increasing moisture, and southeasterly winds, will almost invariably be followed by foul weather, with northeasterly gales continuing for some time after the barometer has begun to rise.. Rapid changes of the barometer foretell brief periods of weather indicated; slow changes, extended periods. The approach of a thunderstorm may be sometimes detected by a slow fall of the barometer, followed by a sudden rise of about 0.05 of an inch upon the arrival of a wind. squall.

Changes of weather upon the lakes follow each other in rapid succession, and the barometer should be read at regular intervals and the reading recorded, especially during the months of October and November, to guard against surprise.

26

NATURE AND CAUSE OF STORMS.

The force of the wind is somewhat greater in the rear of a storm than in front, while its center, or region of lowest barometer, has a movement of its own, bearing with it the whole system of incurving winds, the result being precisely similar to the manner in which an eddy is carried onward by the current of a river. The velocity of this motion, which is greater for continental than for oceanic storms, varies from month to month, being at its maximum in winter and minimum in summer.

Nature and cause of storms and barometric changes attending them.-Upon the weather map published for each day by the United States Weather Bureau, there will in general appear one or more approximately circular areas, marked "low," while others, of rather more irregular outline, will be marked "high," the two alternating, one with the other. The first implies that the reading of the barometer within the area indicated is below the average, the second, that it is above it. If we examine a number of these charts from day to day in succession, we will note that the position of the center of each of these areas upon any particular day is considerably to the eastward of that of the day previous; i. e., there is a rapid easterly motion of both lows and highs, continuing, in the case of the former, until they either fill up or disappear over the Atlantic. The presence of these " "lows 99 exercises a very direct influence over the weather of the region throughout which they prevail. Ordinarily, during the season of lake navigation, they are felt merely as periods of warm rainy weather; in exceptional cases they deepen; i. e., the barometer falls far below the average, under which circumstances they are attended by the rough weather and heavy gales, which constitute a storm.

As these lows approach from the westward, barometers in advance of them are gradually depressed below the mean, generally at a sufficient interval before the appearance of the worst features of the storm to allow the mariner to take proper measures for encountering it. It is upon the barometer, therefore, that he must mainly rely for notice of the storm's approach.

As long as the barometer continues to read within a few hundredths of the average pressure, no decided change in the weather may be anticipated. It is, however, when the pressure starts to rise or fall that the indications of the instrument become of value, as betokening approaching changes, a rise being apt to be followed by an improvement in the general weather conditions, a fall by the reverse. Should the fall continue and be accompanied by other symptoms, such as a southeasterly wind and an increase in temperature, it is safe to count upon a period of stormy weather.

Storms are due primarily to the formation and persistence of areas of low barometer. Under ordinary circumstances, the reading of