516 BEPORX — 1881. 



in" rain-power in the various conditions in which it is presented, whether in 

 rapidly-flowing rivers, in natural waterfalls, or stored at heights in natural lakes 

 or artificial reservoirs. Improvements and fresh inventions of machines of this class 

 still go on ; and some of the finest principles of mathematical hydrodjnamics have, 

 in the lifetime of the British Association, and, to a considerable degree, with its 

 assistance, been put in requisition for perfecting the theory of hydraulic mechanism 



and extending its practical applications. , . , , 



A first question occurs : Are we necessarily limited to such natural sources ot 

 water-power as are supplied by rain falling on hill-country, or may we look to the 

 collection of rain-water in tanks placed artificially at sufficient heights over flat 

 country to supply motive power economically by driving water-wheels ? To answer 

 it : Suppose a height of 100 metres, which is very large for any practicable build- 

 ino- or for columns erected to support tanks; and suppose the annual rainfall to be 

 three-quarters of a metre (30 inches). The annual yield of energy would be 75 

 metre-tons per square metre of the tank. Now one horse-power for 365 times 24 

 hours is 236,500 foot-tons ; and therefore (dividing this by 75) we find 3,153 

 square metres as the area of our supposed tank required for a continuous- supply of 

 one horse-power. The prime cost of any such structure, not to speak of the value 

 of the land which it would cover, is utterly prohibitory of any such plan for utilis- 

 ino- the motive power of rain. We may or may not look forward hopefully to the 

 time when windmills will again ' lend revolving animation ' to a dull fiat country ; 

 but we certainly need not be afraid that the scene will be marred by forests of iron 

 columns taking the place of natural trees, and gigantic tanks overshadowing the 

 fields and blackening the horizon. 



To use rain-power economically on any considerable scale we must look to the 

 natural drainage of hill country, and take the water where we find it either actually 

 falling or stored up and ready 'to fall when a short artificial channel or pipe can be 

 provided for it at moderate cost. The expense of aqueducts, or of underground 

 water-pipes, to carry water to any great distance — any distance of more than a few 

 miles or a few hundred yards — is much too great for economy when the yield to be 

 provided for is power ; and such works can only be undertaken when the water itself 

 IS what is wanted. Incidentally, in connection with the water-supply of towns, 

 some part of the energy due to the head at which it is supplied may be used for 

 power. There are, however, but few cases (I know of none except Greenock) in 

 which" the energy to spare over and above that devoted to bringing the water to 

 where it is wanted, and causing it to flow fast enough for convenience at every 

 opened tap in every house or factory, is enough to make it worth while to make 

 arrangements for letting the water-power be used without wasting the water-sub- 

 stance. The cases in which water-power is taken from a town supply are generally 

 verv small, such as working the bellows of an organ, or 'hair-brushing by ma- 

 chinery,' and involve simply throwing away the used water. The cost of energy 

 thus obtained must be something enormous in proportion to the actual quantity of 

 the energy, and it is only the smallness of the quantity that allows the convenience 

 of havingit when wanted at any moment, to be so dearly bought. 



For anything of great work by rain-power, the water-wheels must be in the 

 place where the water-supply with natural fall is found. Such places are gener- 

 allv far from great towns, and the time is not yet come when great towns grow 

 bvnatural selection beside waterfalls, for power ; as they grow beside navigable 

 rivers for shipping. Thus hitherto the use of water-power has been confined 

 chieflv to isolated factories which can be conveniently placed and economically 

 vforked in the neighbourhood of natural waterfalls. But the splendid suggestion 

 made about three years ago by Mr. Siemens in his presidential address to the In- 

 stitution of Mechanical Engineers, that the power of Niagara might be utilised, by 

 transmitting it electrically to great distances, has given quite a fresh departure for 

 desion in respect to economy of rain-power. From the time of Joule's experi- 

 mental electro-magnetic engines developing 90 per cent, of the energy of a Voltaic 

 battery in the form of weights raised, and the theory of the electro-magnetic trans- 

 mission of energy completed thirty years ago on the foundation aff"orded by the 

 train of experimental and theoretical investigations by which he established his 



