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NEW YORK STATE MUSEUM 



In the beginning of his first paper Bazin remarks that the the- 

 ory of the weir is the least advanced of all branches of hydraulics. 

 The coefficients used in practice vary between such wide limits 

 that in most cases we are unable to make a rational selection 

 from the many numerical values assigned to them. 



The problem, he says, is in fact a complicated one, being con- 

 nected on the one hand with the theory of flow through orifices 

 and on the other with that of open channels. The value of the 

 coefficients in each case is influenced by many elements. Thus 

 we ought to consider: 



1) The velocity of approach; that is, the velocity with which 

 the upstream water readies the weir, the effect of which can not 

 be neglected in weirs of small bight. 



2) The contraction of the vertical section of the stream at the 

 weir, the amount depending upon the hight of the weir and the 

 form of the crest. 



3) The lateral contraction which, though unimportant in weirs 

 of great length, seriously modifies the results in shorter weirs. 



As a further condition. Bazin points out that when the down- 

 stream channel has a width of the length of the weir, so that the 

 overflowing sheet of water, or nappe, touches at the sides, thus 

 preventing free admission of air under the nappe, there occur 

 special phenomena greatly affecting the flow. 1 



Bazin's method of experimentation may be referred to briefly. 

 A standard weir was set up at the head of a long chamber, in 

 which the actual volume passing over Avas measured a sufficient 

 number of times to give averages, which Bazin considers are 

 accurate to within probably less than 1 per cent. Having estab- 

 lished in this way the values of the coefficients for a standard 

 weir, with heads varying from about 0.164 ft. to 1.969 ft., the 

 experiments on weirs of irregular profiles were made by placing 



l Bazin's earlier papers are directed specially to a detailed investigation 

 of these several points. Space will not be taken here to describe his experi- 

 ments in detail. The original data may be found in the Annates des Fonts ct 

 Chavssccs for the years already cited. A translation of the earlier num- 

 bers has also been made by Messrs. Arthur Marichal and John C. Traut- 

 wine Jr., and may be found in the Proceedings of the Engineers' Club of 

 Philadelphia for January, 18lk); July. 1S92: October. 1S92, and April, 1893. 



