MEMOIR ON BOSTON HARBOR. 105 



in the height of water in this channel was only -^, ^, -^, -^, and i, respectively. And, 

 by a contrary proceeding, if several tributary streams are successively let off, the dimen- 

 sions in the height of water in the receiving channel are found to prevail in the same pro- 

 portion as the augmentations.* Experiments by Gennete, Guglielmini, Pitot, and Bossut 

 establish the same fact in nature ; that is, that the effect of the affluent, especially where 

 it seconds by its direction the thread of the receiving stream by making with it a very 

 acute angle, is not to augment materially the section of the latter, but to give to the 

 combined current a velocity approximating nearly to the sum of the velocities of the trib- 

 utary and recipient. 



3. This result from the union of several channels into one, or the concentration into 

 one channel of a volume of water which has previously escaped through several channels, 

 in producing an augmented velocity, leads to the statement of a third fundamental prin- 

 ciple ; which is, — 



The limitation of the channels with a due regard to this : that the velocity be not in- 

 creased to a degree that VA'ould be inconvenient to navigation. 



4. And as, in the case of a tidal stream, the water that passes through all its sec- 

 tions in equal spaces of time will be equal for every part of the channel, or, in other 

 words, as the medium velocities in the different sections of the channel will necessarily 

 be proportional to the amplitude of the sections,! we arrive at the fourth fundamental 

 principle ; which is, — 



That the volumes and mean and extreme velocities of the water passing through the 

 narrowest part of the new or improved channels, at ordinary, extraordinary, and mean 

 states of the tide, are to be calculated and used as strict guides in the projected plans 

 of operation. And 



5. As obstructions in the natural flow of the water lead to a destruction of that uni- 

 formity in the mean velocities in which the accelerating force is equal to the retardations, 

 and consequently to sudden and violent states of the current, and as such obstructions 

 create eddies which destroy a part of the moving force of the current on the borders 

 of the channel, and give rise to conditions favorable to deposit, so we are led to a fifth 

 fundamental principle ; which is, — 



The adoption of such forms for the channel as give an uninterrupted flow to the 

 water ; and these forms must be derived, and can only safely be derived, from observa- 

 tions, f And further, — 



• Gennete's experiments, cited in the Report on Hydraulics. Proceedings of British Association, Vol. III. 

 t Abbe Mann, Castelli, &c. 

 J A. I. C. de Fontaine. 



