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SCIENCE AND INDUSTRY. 
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is much greater than at neap tides. In the case of the Severn, for 
example, the working head at springs would be twice as great as at 
neaps, and the energy output per tide would be four times as great at 
springs as at neaps, while at St. Malo the output would be 5.5 times as 
' great at springs as at neaps. 
Not only is the installation subject to this cyclical fluctuation of 
head, but in any simple scheme the turbines also cease to operate for a 
more or less extended period on each tide; and as this idle period 
depends on the time of ebb or flood tide it gradually works around the 
clock, and will, at regular intervals, be included in the normal indus- 
trial working day. It is true that schemes of operation such as have 
‘been indicated are feasible in which this idle period may be eliminated _ 
and continuous operation insured, but only at a considerable reduction 
of output per square mile of tidal basin area. Even in such schemes, 
- unless the working head is fixed with reference to the tidal range at 
neap tides, the variation of head between springs and neaps causes the 
output to be very variable. s 
In any installation, then, designed for an ordinary industrial load, 
unless the output is cut down to that obtainable under the minimum 
head available at the worst period of a neap tide, in which case only a 
very small fraction of the total available energy is utilized and the cost 
of the necessary engineering works per horse-power will, except in 
exceptionally favorable circumstances, be prohibitive, some form of 
storage system forms an essential feature of the scheme. 
Various storage systems have been suggested. Electrical accumu- 
lators must be ruled out, if only on account of the cost, and the same 
applies to all systems making use of compressed air. The only feasible 
system appears to consist of a storage reservoir above the level of the | 
tidal’ basin. Whenever the output of the primary turbines exceeds the 
industrial demand, the excess energy is utilized to pump water into the 
reservoir, and wlien the demand exceeds the output from the primary 
turbines it is supplied by a series of generators driven by a battery of 
secondary turbines operated by the water from the storage reservoir, 
Evidently this method is available only when the physical configura- 
tion of the district affords a suitable reservoir site within a reasonable | 
distance of the tidal basin. Unfortunately also, considerable losses are 
inevitable in the process, and the energy available at the switchboard 
of this secondary station is only about 50 per cent. of the energy of the - 
water utilized by the primary turbines. Where two tidal schemes at 
some distance apart differ sufficiently in phase, it is possible, by working 
the two in conjunction, to reduce or eliminate the idle period between 
tides, and thus to reduce the necessary storage somewhat; but this does 
not affect the necessity of storage as between spring and neap tides. 
Since storage reduces the available output by one-half, and at the 
same time complicates the system, besides adding considerably to the 
first cost and maintenance charges, the prospects of tidal-power schemes 
would be much more promising if the whole of the output could be 
utilized as it is generated. By feeding into a distributing main in con- 
junction with a large steam station and/or inland water-power scheme, 
and delivering to an industrial district capable of absorbing a compara- 
tively large night load, such a state of affairs might be realized, at all 
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