SCIENCE AND INDUSTRY. 
working head is approximately one-half the tidal range, and the cycle of 
operations under these conditions, and with a constant rate of fall in 
the tidal basin, is shown in Fig. 1. Here the dotted sine curve repre- 
sents the level of the sea on a time base. The working period extends 
from A to B. 
'-’(b) A single tidal basin is used, with the turbines operating on both 
rising and falling tides: The cycle of operations is now indicated in 
Fig. 2. The working period per complete tide extends from A to B 
and from C to D. . Slightly before low water, at B; the basin is emptied 
Fig 2 
through sluice-gates, and at D, a little before high water, the basin is 
filled through the sluice-gates. With a working head equal to one-half 
the tidal range, the period of operation is approximately 50 per cent. 
greater than in system (a), and the: work done per complete tide is 
approximately 50 per cent. greater. 
--(c) A single tidal basin is used with the turbines operating on both 
rising and falling tides. Instead of filling and emptying the tidal basin 
through slnice-gates at high and low water, and working under an 
approximately constant head, the water is allowed to flow through the 
turbines and to adjust its own level. Under these conditions the rise 
and fall inside the basin are cyclical, with the same period as the tide, 
but with a smaller rise and fall and with a certain time-lag. The range 
in-the basin and the time-lag depend on the ratio of the surface area_of 
the basin and of the effective discharge area of the turbines. The work- 
ing head during each tide varies from zero to a maximum. The cycle 
of operations is shown in Fig. 3. The working period is from A to B 
and from © to D,.where the head at the points A, B, C, and D is the 
minimum under which the turbines will operate. The total working 
period per tide is greater than with either of the preceding! systems, and 
the possible output is somewhat greater. On the other hand, the varia- 
tion of head during any one tide is very large. 
. Bigess . rea) 
“(d) Two tidal basins of approximately equal areas are used, with 
turbines in the dividing wall. Each basin communicates with the sea 
502, 
