June 17, 1922J 



NA TURE 



767 



be opportunity, and only the combers, spinners, and 

 manufacturers can give this. 



We have confidence that the necessary opportunity 

 \ ill be given to the well-trained man, and we therefore 

 specially direct the attention of those eligible for the 

 fellowships and scholarships offered by the British 

 Research Association for the Woollen and Worsted 

 Industries. In each case awards are tenable in the 

 first place for one year, and maintenance grants are 

 offered, the maximum value of the fellowships being 

 fixed at 200Z. per annum. Applications for fellowships, 

 which should reach the secretary of the association at 

 Torridon, Headingley, Leeds, before June 30, should 

 contain full particulars of the candidates' training and 

 an outline of the research which it is proposed to under- 

 take. It should be realised, however, that if success 

 is to be achieved a type of " researcher " different from 

 any yet produced is necessary. The man of science 

 has as yet made little or no direct impression upon the 

 woollen and worsted industries ; all the advances made 

 — and these have been more considerable than most 

 people realise at the present moment — have been at the 

 hands of the technologist. Indeed, it is still a moot 

 point as to whether the technologist should be en- 

 couraged to obtain a training in pure science, or whether 

 the man of science should become a technologist. 

 Possibly both these lines of action are promising, but 

 from the scientific point of view it is very desirable that 

 prospective candidates should have a sound knowledge 

 of the industry, for with this knowledge and deeper 

 insight will undoubtedly come a profound respect for 

 an industry which has already achieved so much, and 

 further an earnest desire to help towards increasing its 

 usefulness in the service of humanity. 



Possibly the textile industries offer most promising 

 fields of research in the direction of physical chemistry ; 

 but applied mathematics, chemistry, zoology, and other 

 of the sciences have also claims which will certainly not 

 be ignored. 



A Manual of Tides. 



Tides and Tidal Streams : A Manual compiled for 

 the Use of Seamen. By Comdr. H. D. Warburg, R.N. 

 Pp. vii + 95. (Cambridge : At the University Press, 

 1922.) 85. 6d. net. 



THE author of this manual is convinced, and 

 not without cause, that the non-harmonic 

 methods of giving and using tidal information at ports 

 not served by complete predictions are obsolete and 

 not trustworthy. These methods assume the simple 

 phenomenon of semi-diurnal tides only and came into 

 prominence because the original workers on tides were 

 NO. 2746, VOL. 109] 



most familiar with the tides in European waters. 

 But in most parts of the world the diurnal tides 

 cannot be neglected, even if they are not of greater 

 importance than the semi-diurnal tides, and at present 

 navigators are not provided with information suitable 

 for the calculation of tidal heights in such places. 

 Commander Warburg suggests that the tides should 

 be represented universally by a few harmonic con- 

 stituents, and that navigators should be taught suit- 

 able methods for getting approximate values of the 

 height of tide at any time by the use of harmonic 

 methods. 



The author gives an explanation of the generation 

 of tides and tidal currents as an introduction to the 

 harmonic methods proposed, and he also explains 

 various tidal phenomena such as the double high- 

 waters experienced on the south coast of England, 

 but these explanations cannot always be commended 

 from the scientific point of view. The phenomenon 

 of double high -waters, incorrectly explained in the 

 manual, has often been explained correctly from Airy 

 onwards {e.g. Sir W. Thomson, Nature, Dec. 19, 

 1878), but the wrong explanation is curiously per- 

 sistent. It is alleged that the cause is in the reflection 

 of the tide wave from the north coast of France and 

 that this " reflected wave " arrives on the south coast 

 of England some six hours later than the " primary 

 wave " ; we thus get, it is said, two waves with 

 their maxima some six hours apart and there- 

 fore two high-waters within six hours of one another. 

 But obviously, or at least from simple trigonometry, 

 two semi-diurnal oscillations, whatever be their relative 

 phases, can only combine to give a semi-diurnal 

 oscillation ; that is, the part played by reflection is 

 to make the resultant phase of the actual oscillation 

 at a given place different from what it would have 

 been if no reflection had taken place. The true cause 

 is the presence of quarter-diurnal oscillations in the 

 primary wave. These are due chiefly to shallow 

 water, and with a free unreflected progressive wave 

 the phases of the semi-diurnal and quarter-diurnal 

 oscillations are such that double high-waters cannot 

 occur ; but if reflection takes place then it is possible 

 to disturb this phase relationship so that the minimum 

 of the resultant quarter-diurnal tide occurs about the 

 time of maximum of the semi-diurnal tide ; we may 

 then get a " double-headed tide," or a very long 

 " stand." The importance of the shallow-water 

 constituent is, however, not limited to double high- 

 water phenomena, which are only extreme cases. 



A brief explanation of the mechanical harmonic 

 method of calculating predictions is given, but the 

 diagram of a tide-predicting machine, however, illus- 

 trates motions which are not strictly harmonic. The 



