AUSTRALIAN COLONIES. 



205 



by considering the length of the weir and the height 

 of the surface of the water over the horizontal edge 

 or crest of the weir as it is usually called. 



In flowing through the opening the stream is con- 

 tracted by reason of the water passing around the 

 edges, so that the area of its cross section is smaller 

 than the area of the opening. With a given opening 

 if we widen and deepen the box to certain limits we 

 increase the contraction; beyond these limits no fur- 

 ther contraction is observed. The contraction is then 

 said to be complete, otherwise it is said to be partial. 

 Where the bottom and sides of the box coincide with 

 the edges of the weir the contraction is said to be 

 suppressed. The suppression may also be accom- 

 plished in other ways. For convenience a weir with 

 complete or nearly complete contraction is usually 

 used. 



Messrs. Flinn and Dyer of the Worcester Polytech- 

 nic school, under the direction of Mr. Clemens 

 Herschel, a prominent hydraulic engineer of New 

 York City, undertook a series of careful experiments 

 at Holyoke, Mass., to test the accuracy of the Cippo- 

 letti weir. Their experiments showed that an error 

 of but slightly over % per cent, might be looked for, 

 providing proper precautions are taken.* The use of 

 this weir simplifies the formula used by Francis, so 

 that the discharge may be expressed as follows: 

 Q = 3.3% 1 h% in which Q = the discharge in cubic 

 feet per second; 1 = the length of the crest of the 

 weir in feet; h = the head expressed in feet and 

 measured several feet up stream from the crest. 



ADVANTAGES OF THE WEIR. 



The principal advantages of the weir are: 



1. Cheapness. 



2. Ease of construction. 



3. Accuracy. 



4. It gives the amount of water flowing in terms 

 understood the world, over. 



5. It is not necessary to maintain a constant head 

 in order to determine the amount of water passing. 



6. A small loss of head (smaller than the Montana 

 statutory inch). 



The only drawback which can be urged against its 

 use is that it requires those who cannot solve an alge- 

 braic formula to use a table. A very slight disadvan- 

 tage to place against so many advantages. 



PRECAUTIONS NECESSARY FOR ACCURATE RESULTS. 



In order to obtain reliable results in measuring 

 water by any method, certain precautions are neces- 



* Trans. Am. Soc. Civil Engineers, July, 1894. 



sary. Where water is measured with a weir the fol- 

 lowing conditions ought to be observed: 



1. The approaching channel should be straight and 

 of uniform cross section, in order to avoid eddies and 

 cross currents, for a distance of not less than fifty feet 

 before reaching the weir. 



2. The formulas assume that the contraction of the 

 escaping jet of water is complete. In order to obtain 

 complete contraction, the weir opening should lie in 

 a plane perpendicular to the direction of the stream; 

 the edges should be sharp on the up-stream side and 

 cut away on the down-stream side so as to reduce the 

 thickness of the edge in contact with the water. To 

 insure perfect contraction the distance from the crest 

 of the weir to the bottom of the channel should be 

 three times the depth of the water flowing over the 

 crest; the crest should also be a distance from either 

 side of the channel equal to twice the depth of water 

 flowing over it. The length of the weir shoiild be 

 three times the depth of the water over the crest and 

 the depth of water on the crest should not be less than 

 three inches. 



3. In order that the velocity of the approaching 

 water may not be excessive, the channel should have 

 an area of cross section of at least seven times the 

 area of the weir opening. 



4. Air should be allowed to circulate freely around 

 the escaping body of water where it leaves the weir. 

 The flow is not impeded by raising the surface of the 

 water in the lower channel, providing it is not raised 

 so far as to prevent free circulation of air entirely 

 around the water issuing from the weir opening. 



5. The height of the surface of the water over the 

 weir should be measured at a point several feet up 

 stream from the weir, so as to avoid the depression 

 which occurs as the water approaches the opening. 



The effect of decreasing the distance of the sides of 

 the weir from the crest is to increase the discharge. 

 Ordinarily if this distance is decreased to a distance 

 equal to the depth of water over the crest, the in- 

 creased discharge amounts to about one per cent. 



A further decrease in the distance increases the dis- 

 charge more rapidly. When the bottom of the chan- 

 nel is below the crest a distance equal to twice the 

 depth of water on the crest, the increase flow ordi- 

 narily amounts to about one per cent. 



Experimenters have not agreed entirely as to the 

 proper allowance to be made as a correction for the 

 velocity of the approaching water. In ordinary prac- 

 tice, if the approaching channel has an area of cross 

 section not less than seven times the area of the weir 

 opening, the error is not sufficient to be worthy of. 

 consideration. 



AUSTRALIAN COLONIES. 



BY W. CLAUDE WILSON. 



SO far there have been no large irrigation en- 

 terprises actually carried out in New South 

 Wales similar to those in the United States or 

 even the neighboring colony of Victoria, nor have we 

 any law under which they can be so constructed, the 

 few cases in which any start has been made having 

 had to get special acts of Parliament passed to auth- 

 orize them. The want of any law which will allow 

 the appropriation of water from our rivers and streams 



has been a great drawback to irrigation enterprise, 

 and where improvements in the shape of dams or 

 weirs across creeks, etc., have been constructed, they 

 are always liable to be, and in some cases have been, 

 destroyed by settlers lower down, and there is no 

 redress. The irrigation has therefore been confined 

 almost wholly to the raising of a little fodder for stock, 

 lucerne in most cases being the crop raised, and to the 

 watering of gardens round the various homesteads and 



