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there are two examples, one showing how to compute the fall of water at London-bridge: but that excellent mathematician's investigation of the rule, by which those examples were wrought, was not printed, altho' he communicated to several of his friends copies thereof. Since that time, it seems as if the problem had in general been forgot, as it has not made its appearance, to my knowledge, in any of the subsequent publications. As it is a problem somewhat curious, tho' not difficult, and its solution not generally known (having seen four different solutions, one of them very imperfect, extracted from the private books of an office in one of the departments of engineering in a neighbouring nation), I thought it might give some entertainment to the curious in these matters, if the whole process were published. In the following investigation, much the same with Mr. Jones's, as the demonstrations of the principles therein used appear to be wanting, they are here attempted to be supplied. 

PRINCIPLES
I. [[underline]]A heavy body, that in the first second of time has fallen the height of a feet; has acquired such a velocity, that, moving uniformly therewith, will in the next second of time move the length of 2a feet. [[/underline]]
II. [[underline]]The spaces run thro; by falling bodies are proportional to one another as the squares of their last or acquired velocities.[[/underline]] These two principles are demonstrated by the writers on mechanics.
III. [[underline]]Water forced out of a larger channel thro' one or more smaller passages, will have the streams thro' those passages contracted in the ratio of[[/underline]] 25 [[underline]]to[[/underline]] 21. This is shown in the 26th prop. of the 2^d book of Newton's Principia. 
IV. [[underline]]In any stream of water, the velocity is such, as would be acquired by the fall of a body from a height above the surface of that stream.[[/underline]] This is evident from the Nature of motion.
V. [[underline]]The velocity of water thro' different passages of the same height, are reciprocally proportional to their breadths.[[/underline]]
For, at sometime, the water must be delivered as fast as it comes; otherwise the bounds would be overflowed. 
At that time, the same quantity, which in any time flows thro' a section in the open chan[[strikethrough]]n[[/strikethrough]]el, is delivered in equal time thro' the narrower passages; or the momentum in the narrow passages must be equal to the momentum in the open chanel; or the rectangle under the section of narrow passages, by their mean velocity, must be equal to the rectangle under the section of the open chanel by its mean velocity. -- Therefore the velocity in the open chanel is to the velocity in the narrower passages, as the section of those passages is to the section of the open chanel. 
But the heights in both sections being equal, the sections