Canon Moseley on the steady Flow of a Liquid. 41 



was carried off by the river Auche. The pipe was formed of 

 planks of poplar nailed lengthwise on wooden frames ; their 

 joints were carefully made water-tight ; and when the pipe was 

 fixedj the space between it and the channel of the stream was 

 filled with earth rammed down. As the water was entirely to 

 fill the pipe,, it was necessary that each end should be under 

 water. A bar was for this purpose provided across the stream 

 at the upper end of the pipe^ so as to keep the level of the water 

 above the mouthy and a dam was made across the stream 20 

 metres below the lower end of the pipe, high enough to keep 

 the water also above the level of that end. The upper edge of 

 this dam could be raised at will, so as to keep the lower end of 

 the pipe (by which the efflux took place) immersed to any re- 

 quired depth. It was by varying the height of this dam that 

 the quantity of water which flowed through the pipe in a given 

 time was made to vary. The end of the pipe by which the 

 water entered it was 129 metres from the point where it was 

 received from the canal into the open channel. Having flowed 



129 metres freely along the open channel of greater section 

 than the pipe, it could not but have acquired a greater amount 

 of vis viva than that with which the water ultimately flowed from 

 the pipe. 



Since — is the effective head of water, where h is the ver- 



tical height of the top over the bottom of the pipe, and the 

 effective height is increased by the barrage which brings the 

 level of the water where it enters the pipe above the top of it, it 

 follows that 7 is diminished by the barrage ; and if there were 

 no other causes operating on the other hand to increase 7, it 

 would necessarily be less than unity. These causes have been 

 before discussed ; one of them is the accumulation during the de- 

 scent of the water through the pipe of the work Uj which it carries 

 away with it. The other is the work Ug expended in the hori- 

 zontal pipe on the water in descending through the reservoir and 

 in entering the pipe. But in this case the water descends through 



130 metres of an open channel of much larger section than the 

 pipe before it enters ; and thus when it enters it has already 

 acquired an amount per cubical unit at least equal to that with 

 which it leaves it ; moreover the difference between the aggre- 

 gate vis viva of the water of the stream and that of the pipe 

 cannot be expended wholly in causing it to boil up to the level 

 of the barrage ; part of it cannot but take effect in aiding the 

 rush of water into the pipe, and thereby increasing the effective 

 height, and thus, instead of increasing y, diminishing it. As to 

 the work U2, that part of it which is due to the resistance to the 

 descent of the liquid before it enters the pipe may obviously in 



