MEMOIR ON BOSTON HARBOR. 107 



line of this construction should be made uniform and continuous, complying at the same 

 time with the principles previously laid down. 



12. When the angle of meeting of two streams is a right angle, or approaches a right 

 angle, a deposit will occur at the place of junction, broad at the base and narrowing 

 towards the external termination, the effect of which is to make, by a natural process, 

 the angle of meeting acute, as in the case of the deposit at the point of union of the 

 Mystic with Chelsea Great Creek. Thence we derive from the observation of nature the 

 eighth principle ; which is, — 



That, where lateral streams are diverted into the main channel, or flow into it, they 

 must be made to enter in a direction coincident with that of the principal current to 

 which they become auxiliary.* 



The ninth principle directs that the effect of the contemplated alterations on the 

 transmission of the tide-wave should be studied. The experiments of Mr. Russell show 

 that the rate of transmission of the tide-wave depends on the form and depth of the 

 channel; and he specifically states the numerical terms of this relation. Now it is ev- 

 idently of importance that the tide-waves should reach, as soon as possible, the highest 

 navigable point in the receptacle ; partly because it will add to the height of the water, 

 and still more because it lengthens the time during which the water will be sufficiently 

 high for navigation. To solve this important problem, we are to make use of the num- 

 bers furnished us by Mr. Russell's experiments. 



The last principle to be specified here is this ; that, as all plans of alteration in the 

 harbor should have for their first object its improvement for the purposes and conven- 

 iences of commerce, so they ought to be made with a careful regard to the wants of har- 

 bor accommodation, and to the best and most permanent interests of the owners and 

 proprietors directly concerned in their execution. 



It was my wish and expectation, when this memoir was begun, to be able to present 

 with it a plan of improvement of the harbor, such as might serve at least as a general 

 basis for the application of the foregoing principles. But any plan worthy of the con- 

 sideration of the Academy, or entitled to public confidence, must be accompanied by 

 observations and calculations, which I have not found leisure or opportunity to make. 

 Plans made in the study, without observations in the field, and without calculations de- 

 termining their consequences, may be very erroneous, and cannot safely be trusted. A 

 reference to the principles laid down in this memoir shows the nature, importance, and 

 objects of these observations and calculations. All the data upon which such a plan is 



* Abbe Mann. 



