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the currents in the formation of Chelsea Flats, in the closing of Shirley Gut, the extension of Brewster Bar, and other prominent alterations which the various surveys of the harbor disclose.

It is our purpose to tabulate all the forces at upwards of sixty points at which we have made systematic observations, and to illustrate our numerical data by diagrams, upon which the results will be represented geometrically. These tables and diagrams are very near their completion, the work of last season being already finished.

Of the field work, there yet remains something to be done. It is desirable that the curves of velocities at the principal bridges of the Charles River should be determined ; and that examinations should be made of the gradual passing from sea to river waters as we ascend the streams — hydrometric observations designed to throw some light on the question of inland supply. When we have collected additional materials, we shall enter into fuller details, and embrace a wider field of inquiry.

When this physical survey was commenced, the importance of dividing the project into several seasons' work was especially set forth ; and the reason assigned was, that our computations must keep pace in some degree with the field work, in order that in closing we might leave no point uncovered, but be possessed of the entire scheme of the harbor. Although by economy of time and means we have been so fortunate as to make nearly one third more observations than projected, the advantage of much of this work will be lost unless the survey can be completed. The portion of the work upon which we have thus far reported, is but a small part of that which was accomplished; a full report can only be drawn up when we are able to fill in the details to which we have referred.

We cannot too strongly urge the importance of completing this work without delay. It would be impossible after the lapse of a very few years to recover the thread of our investigations and resume our studies, without going over much of the ground already traversed, which would add greatly to the expense.

The harbor is undergoing a change of regimen by the action of artificial, as well as natural causes, and to obtain a comprehensive view of the intimate relations of phenomena from point to point, the observations at different stations should follow each other in as rapid succession as possible.

JOS. G. TOTTEN,

Bt. Brig.-Gen. U. S. A. Chief Engr.

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28ft. 2.77

· 16

S. Chan'l Ent. to Broad Sound...

11 55

18 21

+ 14

1.46

71

1.89

242

5 52

6 26

1

7

2.30

245

240

2.30

245

66

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TABLE No. 1. - CURRENTS OF BOSTON HARBOR (continued).

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