324 Mr. W. A. Tait [March 4, 



low water to high water, and the same period to fall again. Let us 

 suppose that the water rises ten feet, and that a hulk of 10,000 tons 

 displacement is floating on it, then it is easy to show that only 

 twenty horse-power will be developed by its rise and fall. We should 

 then require ten such hulks to develop as much work as would be 

 given by a steam-engine of very moderate size, and the expense of 

 the installation would be far better bestowed on water-wheels in 

 rivers, or on windmills. I am glad to say that the projector of this 

 scheme gave it up when its relative insignificance was pointed out 

 to him. It is the only instance of which I ever heard where an 

 inventor was deterred by the impracticability of his plan. 



" We may then fairly conclude that with existing mechanical 

 appliances, the attempt to utilise the tide on an open coast is futile ; 

 but where a large area of tidal water can be easily trapped at high 

 water, its fall may be made to work mill-wheels or turbines with 

 advantage. The expense of building long jetties to catch the water 

 is prohibitive, and therefore tide mills are only practicable where 

 there exists an easily adaptable configuration of shoals in an estuary. 

 There are no doubt many such mills in the world, but the only one 

 which I happen to have seen is at Bembridge, in the Isle of Wight. 

 At this place embankments formed in the natural shoals are fur- 

 nished with lock-gates, and enclose many acres of tidal water. 

 The gates open automatically with the rising tide, and the incipient 

 outward current, at the turn of the tide, closes the gates again so 

 that the water is trapped. The water then works a mill-wheel of 

 moderate size. When we reflect on the intermittence of work from 

 low water to high water, and the great inequality of work with 

 springs and neaps, it may be doubted whether this mill is worth the 

 expense of retaining the embankments and lock gates. 



" We see then that, notwithstanding the boundless energy of the 

 tide, rivers and wind and fuel are likely for all time to be incom- 

 parably more important for the use of mankind." 



It is suggested that the Severn is better adapted to the production 

 of power than any other known British river on account of : — 



1. The high rise of tide. 



2. The considerable body of water above the site of the pro- 

 posed dam. 



One objection to the proposed high-level bridge at the Beachley 

 site is that it would be necessary to carry the rails over the 

 Rivers Wye and Severn at an elevation of about 140 feet above 

 Ordnance datum. This would entail a fairly long gradient on the 

 English side leading up to the bridge, and a still longer gradient on 

 the Welsh side. 



Objection is taken to the suggested provision of an opening- 

 bridge on the low-level line at the tunnel site. This, however, is 

 partly answered by the fact that until there is a barrage, shipping 

 generally, but particularly small craft, can only make very limited 



