MOTION AND RESISTANCE OF FLUIDS 3Q1 



tvil motion of the fluid towards the orifice accelerates the velocity 

 after it escapes from the vessel by contracting the stream, yet it 

 must diminish the velocity at the orifice; that is, if the same per- 

 pendicular motion were to take place without the horizontal mo- 

 tion, the fluid would flow out faster ; for as any motion in a fluid 

 is immediately communicated in every direction, the horizontal mo- 

 tion will produce a motion upwards, and in some decree obstruct 

 the descent of the fluid. If therefore this horizontal motion could 

 be taken away, or any how diminished, the fluid would flow out with 

 a greater velocity. Now if a pipe be fixed, the fluid at the bottom; 

 of the vessel flowing towards the orifice will, by its adherence to the 

 vessel, continue to adhere to the sides of tiie pipe as soon as it ar- 

 rives there, and by this means almost all the horizontal motion will 

 be destroyed, and converted into a perpendicular motion; for the 

 horizontal motion arises principally from the fluid which flows from 

 and very near to the bottom, where the whole motion is very nearly 

 in that direction. This motion therefore being thus nearly de- 

 stroyed, the fluid will be less interrupted at the orifice, and conse- 

 quently will flow out with a greater velocity. But why the velocity 

 should also be increased either by increasing the length of the pipe, 

 or making it an increasing cone, under certain limitations, is a cir- 

 cumstance which, I confess, I can give no satisfactory reason for. 



The above-mentioned experiments were made principally with a 

 view to ascertain how far the theory of the motion of fluids can be 

 applied ; and the inquiry has led to several circumstances which 

 probably have not been observed before. That the theory is not 

 applicable in all cases, is manifest ; but that it brings out conclusions 

 in many instances which agree very well with eNperiment, is un- 

 doubtedly true. This tends to show, either that the common prin- 

 ciples of motion cannot be applied to fluids, and that the agreement 

 is accidental ; or that under, certain circumstances and restrictions 

 the application is just. Which of these is the case, is not perhaps 

 easy for the mind to satisfy itself about. Nothing however which is 

 here said, is done with any view to detract from the merit of those 

 celebrated authors. They have manifested uncommon penetration, 

 and carried their inquiries on the subject to an extent, that notiiine 

 farther can be hoped for or expected ; and if they had done no- 

 thing else in science, this alone would have ranked them among 



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