104 MEMOIR ON BOSTON HARBOR. 



experiment, and resting on the highest authority, a water receptacle of one hundred and 

 eighty acres in area, having eight feet of water on it, wliich it receives, on the average, 

 at every flow of the tide, would only be equal to one of eighty-four acres, receiving and 

 having ten feet, that is, would only be equal to it in power to keep the channel clean 

 and sweep away the loose deposits. 



This question of the conservation of the reservoirs is to be treated relatively as well 

 as absolutely. During an examination before a committee of the House of Commons, 

 the following interrogatory was put to ]\Ir. John Scott Russell by Mr. Hume : " Do you 

 mean to say that a considerable portion of land might have been inclosed, provided com- 

 pensation had been made by an addition of water by deepening the channel ? " To 

 which Mr. Russell replied, " Perfectly so ! " 



But the fact that the diminution of the reservoir leads to the diminution of the chan- 

 nels, a smaller quantity of water with less velocity requiring less water-passage, conducts, 

 by an inverse process of reasoning, to the second principle : — 



The contraction of the water-passage, or the union of the waters into one channel, 

 and the cutting off of the secondary and lateral channels which conduct the water 

 away from the main channel, and destroy its power and usefulness by wasteful diffusion.* 



But while putting into practice the second principle, there are some subordinate 

 principles, the effects of which are to be observed, and which lead to other fundamental 

 principles. 



1. When the waters flowing in several channels are united into one channel, the ca- 

 pacity of the latter will be less than the sum of the capacities of all the channels, before 

 the union was made ; that is to say, the union of the different passages into one will not 

 lead to a corresponding augmentation in this single passage. This is established by ex- 

 periment, and confirmed by observation in nature. 



2. The apparent contradiction contained in the above statement is explained by the 

 augmentation of the velocity in the main passage, which, under the most favorable cir- 

 cumstances, 7night be equal to the sum of the velocities in original channels.f 



It has been found, for example, by experiment, that, if a stream equal to one half the 

 water in the receiving or main channel was added, and afterwards another half, the 

 quantities in the receiving channel being successively 1, H, 2, the height in the latter 

 was apparently the same, while the velocities and quantities of the fluid increased in 

 the same proportion; namely, 1, H, 2. Again, when the augmentations to the 

 quantity in the receiving channel were in the ratios of 3, 4, 5, 6, and 7, the increase 



* A. 1. C. de Fontaine. t Guglielmini. 



