PKESlDKXriAI. .\l)L)Ki;SS— SECTION A. 



37 



grinding' of corn, and for nian\ ccnlnries these remained the only 

 anxih'aries to animal power. Althongh water-wheels were gradit- 

 all\' im])rove(l. they still remained inefficient and cumbrons 

 machines and of com[)aratively low ])ower, since they are incap- 

 able of ntilising high falls. The largest water-wheel ever erected 

 ('at I.axey. Isle of .Man) (shown in h^ig. 22) was 72 ft. 

 in diameter and develo])ed 150 h.]). The introduction 

 of steam ])ower. towards the end of the eighteenth cen-" 

 tnr_\-, caused water power to be greatly neglected, but 

 the development in recent years has been trulv remark- 

 able, due in the hrst j)lace to the gradual imi)rovement of 

 the hydraulic turbine (invented "about 1840), making it possible 

 for larger and higher waterfalls to be harnessed, but mainly 

 to the ])ossibility of long-distance electrical transmission on an 

 economical basis. enal)linir reu'iote sottrces of enero\- to be bi-ought 



Fn 



. — Overs!nJt Water-wheel at Laxc\-, Isle of Man. 



to industrial centres; but the use of electricity for chemical and 

 metallurgical [)urposes has done more than anything else 

 to focus jniblic attention on water-power schemes — indeed. man\' 

 chemical manufactures are only possible due to cheap electric 

 power obtained hydraulically. It is estimated that the total 

 capital invested in hydraulic i)Ower inidertakings in the world 

 is probabl)- over £500,000,000 at the present day. 



Although water power owes its origin to evaporation by the 

 sun, hydraulic turbines receive their energy in the mechanical 

 form without any intermediate state of transformation, as in 

 the case of heat engines, which convert heat energ}' into mechani- 

 cal work. Efficiencies of 80 per cent, are easily obtainable, and 

 hydraulic turbines are now made in single units up to 20,000 h.p. 

 Improvements now enable high heads as well as low heads to be 



