2l8 



NA TURE 



[July 5, 1906 



are here confused, the henotlicism (as it is called) of 

 the earlier period of Jewish history which regarded 

 Jehovah only as one among many Gods, the one who 

 fought on the side of the Israelites, and who ought 

 to be worshipped by them ; and, contrasted with it, 

 the later and truly monotheistic ideal of the prophets, 

 which emphasised the solitv of Jehovah. It would, at 

 any rate, be difficult to harmonise our author's account 

 with any of the accepted readings of Jewish history, 

 traditional or critical. Part of the page ought 

 probably to be re-written. 



TIDES AND WAVES. 



A Practical Manual of Tides and Waves. By W. H. 

 Wheeler. Pp. viii-l-201. (London : Longmans, 

 Green and Co., 1906.) Price ys. 6d. net. 



THE author of this book is a well-known civil 

 engineer, whose practice has been largely con- 

 cerned with works on the sea coast and tidal rivers. 

 The practical side of the subject treated has conse- 

 quently required and received from him long and 

 close study ; his intention in this volume has been " to 

 give as practical an account as possible, free from all 

 mathematical demonstration, of the action of the sun 

 and moon in producing the tides : and of the physical 

 causes by which the tides are affected after their 

 generation, and of their propagation throughout the 

 tidal waters of the earth." To these subjects the 

 principal portion of the work is devoted; in a com- 

 paratively short section the author deals also with 

 wave phenomena, in a manner likely to be useful to 

 practising engineers, and not lacking in interest to 

 a much wider circle of readers. Mr. Wheeler has given 

 much time and thought to the production of the work, 

 and the bibliography of his subjects (contained in an 

 appendix) indicates a wide range of reading. In the 

 te.\t itself a great mass of useful information and data 

 is summarised; this is supplemented by several 

 valuable appendices giving results of tidal and wave 

 observations as well as formulae of use in engineering 

 practice. A good index makes reference easy to the 

 principal features of the book, and adds much to its 

 value to readers for whom it has been chiefly designed. 

 In one particular the scheme of the author is open to 

 criticism : he has aimed at making " the subjects dealt 

 with in the separate chapters complete," and this has 

 involved some repetition of statement. Probably the 

 explanation is that in some cases papers prepared for 

 separate publication have been embodied in the book ; 

 but although the repetition (as the author says) may 

 have " been avoided as much as possible," his scheme 

 for completeness in individual chapters necessarily in- 

 volves it, and in a book such as this is the result 

 is not altogether satisfactory. This is a small draw- 

 back, however, to a work of considerable merit that 

 will undoubtedly be welcomed by the engineering 

 profession as a book of reference bringing together 

 within small compass a great mass of useful informa- 

 tion drawn from widely-scattered sources. 



A historical sketch of the development of tidal 

 science is first given ranging from the work of 

 NO. 1 914, VOL. 74] 



Copernicus to that of Sir George Darwin and Mr. 

 Moxly. Next come descriptions in popular language 

 of "the making of the tides," the "propagation of 

 the tidal wave," and the mean level of the sea and 

 range of the tides. All these subjects are illustrated 

 by facts and figures drawn from actual observations. 

 The effect of wind and atmospheric pressure on the 

 tides is considered at some length, as a matter of 

 considerable importance to engineers. Mr. Wheeler 

 has endeavoured to formulate a rule as to variations 

 to be expected with a given force of wind and height 

 of tide ; and considers that roughly " the effect of a 

 moderate gale is to raise or lower the tide according 

 to its direction as many inches as it would rise in feet 

 under normal conditions." He gives some striking 

 instances of abnormal tides due to gales of long con- 

 tinuance, the heights attained in some cases exceeding 

 the tide-table heights by six to eight feet. In 

 December, 1904, for example, at Grimsby, the morn- 

 ing tide was raised nearly seven feet, and at Hull, as 

 well as on the Thames, about five feet above normal 

 level by a heavy gale from the north-west. An in- 

 vestigation is also made of the recorded observations 

 of variations in tides accompanying variations in 

 atmospheric pressure, and the conclusion is reached 

 that " it is not possible to lay down any general law 

 applying to all parts of tidal waters." Mr. Wheeler 

 considers that " although variation in pressure may 

 be a primary cause of the alteration in the height of 

 tides . . . yet the wind is a safer and more ready 

 guide for the immediate purpose of navigation." 



The chapter dealing with " River Tides " is one of 

 the most interesting in the book, and from the nature 

 of the case is chiefly based on actual observations. 

 Mr. Wheeler traces the progress of the ocean tidal wave 

 up a river channel, and shows how the distance to 

 which the wave action reaches depends on the condi- 

 tion of the channel and the depth of the low-water 

 stream. He describes the " ponding back " of the 

 current in the river by the advance of the tidal wave, 

 and demonstrates the necessity for the duration of 

 the flood tide in rivers being less than that of the ebb. 

 The phenomena of " double flow " are explained, 

 and a distinction made between the propagation 

 of a tidal wave up a river and the tidal current. 

 These movements of river water are accompanied 

 by transport of material carried in suspension, and 

 from the engineering side this is a question of 

 great importance which Mr. Wheeler discusses fully. 



Closely related to tidal currents are tidal "bores," 

 which occur in certain rivers. These are very fully 

 described by the author, who summarises the condi- 

 tions necessary for the full development of a bore as 

 follows : — A considerable rise of tide, a converging 

 channel with a rising bed, the depth of water decreas- 

 ing as the channel is approached, or a sand bar over 

 which there is not sufficient depth of water to admit 

 of the passage of the approaching tidal wave. Under 

 these conditions, in place of a gradual rise of the water 

 at the entrance to the river, the arrival of the tide is 

 accompanied by a breaking wave with a crest several 

 feet in height, which when formed advances rapidly 

 up the channel. In the Tsien-Tang-Kiang River, 



