December 30, 1920] 



NATURE 



559 



Egfvpt from basin to the f>erenniaj system of 

 irrigation is now due, and to meet these needs 

 this barrage will have to be constructed. 



Besides these works which are about to be 

 constructed on the Blue and White Niles, two 

 other projects of which the need in the future 

 can be foreseen to complete the control of the N'ile 

 supply are briefly discussed. One of these is 

 the Lake .Albert dam, by means of which 

 it is proposed to hold up a reserve store of 

 water in the -•Vlbert Lake, which will be con- 

 \eyed to the White Nile by a channel or channels 

 so planned as to avoid the loss of water which 

 now takes place in wide, shallow valleys where 

 the sadd marshes are situated. The other scheme, 

 which is even more briefly outlined, is the pro- 

 vision of a dam on the upjjer reaches of the Blue 

 Nile to store 7000 million cubic metres of water, 



» of which part would be kept as a permanent re- 

 serve in case of low floods, and the balance 

 usi'd to irrigate the cotton crop on one-third 

 of a million feddan area in the Sudan. Nothing 



s has yet been done on either of these projects, and 

 no details are published in the report; they are 

 only indicated as works which must eventually be 

 undertaken to provide the necessary water for 

 agriculture in arid and semi-arid areas of the 

 Nile basin. 



The report contains a large amount of valuable 

 information on the utilisation of water under the 

 special conditions which prevail in Egypt. The 

 requirements of agriculture are fully stated by 

 the responsible authorities of Egypt and the 

 Sudan ; detailed estimates of the amount of water 

 which is available at various seasons are also 

 given as the result of a long series of measure- 



tmcnts which have been made in recent years. 

 This collection of hydrographical data brings 

 those which were previously available up to date, 

 ,md supplements them by much information of 

 reater accuracy on which the present projects 

 have been based. 



With a rapidly increasing population the occa- 

 sional <Kcurrcnce of such disastrously low floods 

 '- that of 191 3 has carefully to be guarded 

 _;ainst; on the other hand, the growing demands 

 of cultivators in Egypt, and the needs of the 



I Sudan, which will be increasing for years to 

 'Come, call for the most careful investigation of 

 the hydrography of the Nile, for, while the supply 

 of water is shown to l)c sufficient to meet all 

 anticipated requirements, this can be done only 

 by a full control of the supply and a careful regu- 

 lation at all seasons by suitable works. 

 NO. 2670, VOL. 106] 



Poynting's Scientific Papers. 



Collected Scientific Papers. By Prof. J. H. 

 Poynting. Pp. xxxii + 768. (Cambridge: .\t 

 the University Press, 1920.) Price 375. 6d. net. 



THESE papers make a stately volume of con- 

 siderably more than 700 pages, and our 

 thanks are due to the editors, Mr. Guy Barlow 

 and Dr. Shakespear, for the ability with which 

 they have performed their work, a work which, 

 as old pupils of Poynting, must have been to them 

 a labour of love. The volume contains an excel- 

 lent portrait, and the type, paper, and binding 

 are worthy of the Cambridge University Press. 

 1 think everyone, even though he may have 

 thought himself well acquainted with Poynting's 

 work, will find here something which he sees for 

 the first time, for the volume includes not only 

 papers from such normal sources as the Trans- 

 actions and Proceedings of the Royal Society and 

 the Philosophical Magasinc, but also others from 

 the India Rubber Journal, the Hibbert Journal, 

 the " Encyclopaedia of Biblical Literature," 

 the Mason College Magazine, and the In- 

 quirer. In addition to the classical papers on 

 the flow of energy in the electromagnetic 

 field, on the pressure of light, and on the 

 density of the earth, there are others on 

 the drunkenness statistics of the large towns, 

 on the fluctuations in the price of wheat, 

 on the experiences of one who overtook the 

 waves of light, a criticism of Herbert Spencer's 

 "First Principles," and a paper on physical law 

 and life. To those who knew Poynting, these in- 

 formal papers have a special charm, for they will 

 find in them much that will recall memories of 

 long-past talks; they recall his quiet humour, the 

 freshness of his views, his courtesy in debate, his 

 dread of saying or doing anything that could hurt 

 the feelings of anyone who did not hold his own 

 views on the point at issue. Among the seventy 

 papers in this book, there are not more than two 

 or three that could be called controversial, and it 

 is characteristic of these that he criticises his 

 opponent as if he loved him; and, even when the 

 author under notice has laid himself more than 

 usually open to criticism, Poynting is not content 

 with pointing out the unsoundness of his state- 

 ments ; he suggests that he must really have meant 

 something else, something much more reasonable. 

 Another feature of the book is that running 

 throughout the papers is a view of the philosophy 

 of physics which is now very prevalent, but which 

 Poynting was one of the first in this country to 

 adopt. This view is summarised in the paper on 

 " Physical I^w and Life " ; and though this paper 



