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and in flowing out the current is similar to the currents of what are known as "rapids" in rivers, where the water is shallow, and where there is a slight declivity in the surface, as there is in the Charles River on each side of the channel; and this shallowness and declivity give an impetus to the water, which it imparts to the deeper water of the harbor, and causes the current to be much stronger and swifter than it otherwise would be as it rushes. towards the sea. The force thus derived from the declivity in the surface of the basin is lost if the basin is never empty, or is so full as to bring the deep water on the same level with the shallow water. It is not necessary to point to the rapids of the St. Lawrence as an example of this principle. Every boy who has fished along the streams of New England has noticed it, and understands the fact of its existence perfectly well.
I contend, therefore, that if an equal quantity of water came in with the tide, its scouring force would be much less if it were confined within a deep narrow canal than it is in the present great harbor basin. But there is another danger to be guarded against less water would flow in, and the force of the current would be proportionately reduced. The rise of the tide in a river or basin depends upon the demand or space there is for the tidal water. Thus frequently the farther up a river we go, the higher the tide rises. At London bridge, the tide rises four or five feet higher than at the Nore, sixty miles farther down; and removing the narrow arches of old London bridge, forty years ago, has had the effect of causing the tide to rise a foot and a half higher than it did before. The same is true of the remarkable tides in the Bay of Fundy. Captain Vaughan, dockmaster at the London docks, gave some very important and interesting evidence upon this point some years ago before a Parliamentary committee, on the subject of the embankment of the Thames, and the necessary precaution required to prevent a consequent injury to the navigability of the river. "If," said he, "you narrow the river from eight hundred to six hun
dred feet, you will lose one-third of the water that now comes up." As the space for tidal water was decreased, so would the rise of the tide be decreased, and its usefulness in carrying away the silt and sewage consequently diminished.
An example of this has been shown by the history of the harbor of Lynn Regis in England, under circumstances so analogous to our own harbor that I must beg leave to make special reference to it. Lynn is situated at the mouth of the river Ouse, which empties into a large bay on the eastern coast of England, known as the Wash. The Ouse flows northerly through a flat marshy country, extending across Cambridgeshire and into Lincolnshire called the Fens, which formerly was so frequently overflowed that the city and adjacent country of Ely are known by the name of the Isle of Ely. Long ago a flood tide extended up to Ely twenty-five miles from Lynn, and at times sixteen miles still farther up to Cambridge. To put an end to the inundation of a large tract of land known as the Bedford level, great dykes were dug fourteen miles above Lynn to receive the water which formerly covered it; the land was drained, and the tidal waters kept in narrow canals; and the consequence was, that the old channel to the sea was lost and the harbor of Lynn almost ruined. The harbor of Lynn may not have been so valuable as the extensive fertile tracts thus rescued to agriculture; but so ignorant were people at that time about the effects of the tide, that the same thing would have been done under similar circumstances behind London or Liverpool, and might have ended in irreparable injury to the kingdom. I beg leave to refer the committee to an interesting article on this subject in Fraser's Magazine, Vol. LXXI. p. 466.
We cannot therefore make a compensation for the space covered by tidal waters by deepening the narrowed channel. At all events it is so uncertain, and this view is sustained by such high authority, that Boston may well dread any such perilous experiments. If I am referred to what already has been done in
Boston harbor, I answer that this process of filling along its shore began two centuries ago, and we have no data whereby we can judge what injury has been done to the harbor, or how much inferior it is now to what it was in the days of Blaxton, Maverick and Winthrop. It is certainly not in a satisfactory condition at present, and my own opinion is, that by an overwhelming preponderance of evidence it is shown to have deteriorated steadily for many years past. If the harbor has been seriously injured, is it unreasonable to assume that the vast encroachments made by man upon the sea, and the consequent reduction of the amount of water which comes in with the tide, have aided in this injury? And is it not our duty to be cautious in permitting these encroachments to be continued?
Another peculiarity of our harbor is the comparative sluggishness of the current. The average velocity of the current of the Thames at London is three miles an hour; the velocity of the current in New York harbor is more than two miles an hour. In Boston it is only one mile an hour. If the velocity of the current measures the scouring force of the water, this force in Boston is only one-half what it is in New York, and onethird what it is in London; and the dangers to our harbor from the silt and sewage increase in inverse ratio.
I shall say but one thing more on this question of the harbor, and then leave it upon the evidence and the arguments of my associates. This is what was stated by Mr. Pratt; that by reducing the velocity of the current you increase the liability of the harbor to freeze in cold weather. This is now prevented by the combined influence of the sea water, which is of a comparatively mild temperature, coming in at every tide, and of the velocity of the current, which prevents its freezing before it flows out again into the open sea; and yet in extremely cold weather it is difficult to prevent its freezing, and every winter the harbor is greatly encumbered with ice, and most of us here have known times when it has been frozen solid enough
for us to pass over it. As you reduce the amount of sea water which comes in, and diminish the velocity of the current, you increase the danger of its freezing. This was so satisfactorily shown by Mr. Pratt that I need not dwell upon it.
But while, gentlemen, there may be differences of opinion among men who are equally well qualified to form one, as to the effect which any considerable encroachment upon the Charles River basin may have on the harbor, it is difficult for me to understand how the impending danger to the sanitary condition of our city can be underrated by any one who has ever resided in a city, or has watched the vast outlays made elsewhere for procuring that fresh air which some among us are so ready to sacrifice. Many experts have been called before you to testify to the influence which the tidal water in Charles River has in cooling the atmosphere of Boston in summer, but I should think that ordinary personal experience would teach all who have passed a summer in Boston the truth of this theory, and as to them have rendered any scientific testimony unnecessary. Ocean water is cooler than the adjacent land; the neighborhood of the sea is generally cooler than territory removed from its influence. Here we have behind our city a large area, which at every tide is filled with this water fresh and cool from the ocean, and which, before it becomes heated, flows out again, and is succeeded by other water of the same uniform temperature. The effect upon the atmosphere above the water, and upon the wind which blows over it, cannot be denied. And I do not care much about whether the wind blowing over it from the west or southwest will sweep over the entire city, or over only a small part of it, the cooling influence of the water will not be seriously changed. Atmosphere is a much better conductor of heat and cold than metal is; yet if we put the end of a metallic rod into a tub of ice, the effect would quickly be perceived in every part of it. Were an iceberg to be anchored in the Charles River, its cooling effect upon the atmosphere all over the city
would soon be felt, whatever might be the direction of the wind; and so, if the influence of the tidal water is to reduce the mean temperature on Charles River ten, fifteen, or twenty degrees, the adjacent atmosphere will feel its influence. But the prevailing winds which blow over Boston in summer (the west and southwest) are still cooled by this water, although not to the same degree which they were before we shut the tide entirely out of the basin south of Beacon street; and although they strike directly the more westerly parts of the city only, their influence upon the currents in the streets has been too long experienced by Bostonians to permit us to doubt its existence. The streets in a city will deflect all winds and, to some extent, change their direction.
I contend, therefore, that the heat of Boston is lessened by the tidal water in Charles River, both because the atmosphere under any circumstances would prove a conductor of the cold engendered by it, and also from its influence on the normal summer winds. The question then presents itself, can we exclude the water from any considerable part of this basin without proportionately lessening this benefit? And I most earnestly contend that we cannot. The great surface covered by the water increases the amount of cold air, because it increases the amount of air brought in contact with the water; while, as I have remarked, the water does not remain in the basin long enough to experience a corresponding change from the Whatever amount of compensation may be obtained for extent of area, by deepening the narrowed channel, so far as the scouring forces in the harbor are concerned, you obtain no such compensation in the respect I am now discussing. Reduce one-half, one-third, one-quarter the water arca, and you proportionately reduce the amount of cool air derived from it.
The appellation given to this harbor basin by Dr. Holmes, of one of the lungs of Boston, was criticized somewhat severely