August 28, 1913] 



NATURE 



667 



salts contained in the anode, and are cast off from 

 the anode at great velocity (ioo to iooo kilometres 

 per second). Difficult measurements carried out 

 have had reference to the velocity and to the 

 ratio of the electric charge to the mass of a 

 luminescent particle for different metals. Views, 

 corroborated chiefly by spectroscopic tests, make 

 it probable that the anode rays are identical with 

 the sun's protuberances — that the latter are 

 nothing but anode rays of gigantic dimensions. 

 The annual report of the Reichsanstalt for the 

 past year, just to hand, gives evidence of con- 

 tinued progress in the various branches of scienti- 

 fic investigation, but space will not permit of 

 touching on the subjects dealt with : readers are 

 referred to the Zeitschrift fur Instrumentenkunde, 

 March, April, and May, 1913, in this connection. 

 E. S. Hodgson. 



DERIVATION OF POWER FROM TIDAL 

 WATERS. 



""THOUSANDS of years have been required to 

 evolve the processes by which the energy 

 stored by natural agencies has been made to fulfil 

 our requirements ; thousands of years may still be 

 required to evolve processes by which the internal 

 heat of the earth, the phenomena attendant on 

 barometric pressure, and the potential energy of 

 the tidal wave may be similarly utilised. 



But with regard to the latter much has in 

 reality been already achieved. Vast fleets of 

 barges and shipping are daily carried to and fro 

 by means of the tidal stream in estuaries and the 

 mouths of rivers. Ships of all sizes are lifted and 

 kept afloat in inland tidal basins. London, 

 Cardiff, Bristol, and numerous seaport towns 

 illustrate the fact that ends impracticable by 

 other means may be attained by the utilisation of 

 the tidal wave ; and there is little doubt that as 

 time goes on, the advantages to be derived from 

 the utilisation of the tides in dock work 

 will be manifested by even greater and more im- 

 portant works than have yet been undertaken. 



Why, then, should it generally be considered 

 impracticable to utilise some small portion of the 

 potential energy of the tidal wave in the produc- 

 tion of energy for other useful purposes? The 

 answer to this question is difficult to find, but it 

 appears that about forty years ago an attempt 

 was made to investigate the matter. An analysis 

 of the initial cost and probable revenue from a 

 tidal installation was made the subject of articles 

 in The Engineer. The result of the analysis 

 showed that electricity could be produced at a 

 cheaper rate with gas engines than by a tidal in- 

 stallation. The cumulative result of this weighty 

 opinion was evidently far-reaching, and for many 

 years only half-hearted attempts have been made 

 to prove that the tidal installation is no longer to 

 be considered outside the range of practical engi- 

 neering problems. 



The conditions which obtained forty years ago 

 are no longer in existence. The improvements in 

 plant for carrying out large works are so great 

 NO. 2287, VOL. 91] 



that they are difficult to realise. The hydro- 

 electric installations in those days were so few in 

 number and so unimportant in effect, that the vast 

 works which have been executed in the past few 

 years would likewise have been considered im- 

 practicable from a commercial point of view, or, at 

 the best, in the light of doubtful experiments. 

 Even so late as 1904, in a paper read before the 

 Institution of Civil Engineers (vol. clvii., session 

 1903-04, part iii.), Mr. Steiger gives it as his 

 opinion that water power has been chiefly used for 

 driving flour mills, and as the authority of the 

 author is above dispute, it may be safely con- 

 cluded that an analysis made forty years ago 

 should no longer be allowed to stand without 

 revision. 



Perhaps the most important modification of the 

 conditions which obtained until quite recently is 

 the use of ferro-concrete as an auxiliary to the 

 formation of embankments. The strength and 

 durability of structures, such as bridges and 

 landing stages, with struts and braces of ferro- 

 concrete has proved the possibilities of that 

 material in braced structural work, while the 

 small section and great length of ferro-concrete 

 piles has shown the possibility of handling suit- 

 ably designed beams and girders of this material 

 without risk of injury to them. 



Now by constructing braced trestles which can 

 be handled by a crane, and placed so accurately 

 in position that slabs of ferro-concrete, designed 

 for the purpose, may be set between them and 

 fixed, an extremely economical shell may be 

 formed to serve as the matrix of an earthwork 

 embankment. 



The present writer has had the privilege of 

 making an exhaustive investigation into modern 

 methods of forming sea walls, wharfs, break- 

 waters, and other sea works of that kind, and he 

 is in a position to state that where there is no 

 danger from the action of heavy seas, great 

 economy can be effected by forming the face of a 

 sea wall with a skin of concrete slabs, held in 

 position by trestles of the same material. 



But even with the saving which can be effected 

 by this method of construction, the tidal installa- 

 tion is only practicable from a commercial view- 

 point when the initial cost can be reduced to be- 

 tween 40/. and 50L per horse-power ; or, stating the 

 matter in another way, unless the sum of the 

 maintenance charges, plus about 10 per cent, on 

 the capital outlay, divided by the capacity of the 

 installation in horse-power, does not exceed 4?. 

 per horse-power year. 



The financial side of the question is of the first 

 importance, but the difficulties to be overcome on 

 the technical side are also, it is to be presumed, 

 regarded as nearly insuperable as well. To deal 

 with the latter it is necessary briefly to consider 

 the general characteristics of tidal waters in 

 estuaries or similar locations, and to indicate the 

 methods proposed for overcoming them. 



When the tidal wave passes from the open sea 

 into the funnel-shaped entrance of a channel or 

 estuary, its volume being constant, the height of 



