32 



l'KKSll)l-:XTrAL AIJDRKSS SKCTION A. 



suggest that the forees of nature will be adapted and made 

 -subservient to the use of man as soon as the enhanced i^rice of 

 coal makes the ])ressure felt. Hie layman has observed the 

 foolish waste of power when the many millions of tons of ship- 

 ping in harljours are raised and lowered lo to 20 feet every 

 dav. and have conseciuenth" tioodcd the world with manv fan- 



FiG. 14. — Suggcsu-d large puwer Windmill. 



tastic schemes for the utilisation of wave and tidal jjower. But 

 they forget that the work' done by tides is only enormous because 

 of its \ast extent, and the time element has to be considered. 

 To raise a vessel of 50,000 tons displacement a vertical distance 

 of 10 feet involves an expenditure of under 85 h.p. if the time 

 taken to do it is six hours. And then it is not fully realised 

 that a considerable fall is necessary, unless an enormous quantity 

 of water is available, to give a useful amount of i)0wer. l-'or 



i'lc. . 15. — \\ aw and tiravity Alotor. 



exam])le, a horse -power inv a da\ ot id liours re(|uires about 

 1.200 tons of watei" falling from a heiglu of 10 feet, so that to 

 develo]) under this lu-ad i.ooo h.p. would re(|uire 1,200,000 tons 

 of water, or over lo.cioo.ooo cubic Uct per day ot 10 hours. 



The less ambititnis schemes ado] it wave-motors, the power 

 being generally utilised to comj)ress air, though sometimes, in 

 all iiuiocence, electric generation has been suggested. 



