I 12 



NATURE 



[November 24, 1910 



of the year's rainfall may, under favourable condi- 

 tions, be stored in the soil for the next year ; thus, if 

 only 15 inches fell each year, making a total of 30 

 inches in the two years, the wheat crop grown during 

 the second year should have moisture available equiva- 

 lent to 25 inches or more, on which, of course, it 

 should do very well. Unfortunately, the rainfall does 

 not necessarily remain near its average, but fluc- 

 tuates considerably, and records are not available for 

 many districts ; it has occurred in districts where dry 

 farming was considered a great success that the rain- 

 fall was, after all, about 20 inches, and ordinary 

 cultivation would have been equally good. 



However, the interesting problem is this : What is 

 function of the compact subsoil and the loose surface 

 layer? It is usual to suppose that the compactness 

 of the subsoil facilitates the upward lift by surface 

 tension of water from the permanent water table, but 

 it would seem equally rational to suppose that the 

 compact subsoil retards the percolation of the water. 

 So far as the writer is aware, no crucial experiments 

 have been made that show beyond doubt how far the 

 upward movernent of water by surface tension is a 

 factor in ministering to the needs of the plant. That 

 it takes place, of course, is not disputed, but its rela- 

 tive importance is unknown. The function of the 

 loose layer on top, the "mulch," is not settled. It is 

 commonly regarded as a break in the structure of the 

 soil leading to a rupture of the "capillary films" of 

 water. It may equally be a non-condticting layer 

 shielding the mass of the soil from the sun's heat, 

 and therefore lessening evaporation. 



Until these problems are solved, little advance can 

 be expected from the scientific point of view, although 

 the practical man continues to effect improvements. 

 The fundamental need seems to be a mathematical 

 analysis showing how water will distribute itself over 

 a mass of particles varying in diameter from below 

 0002 mm. up to o"i mm., the bulk being below o'oi 

 mm., and how rapidly any disturbance in equilibriuni 

 will readjust itself. The pressing need of work in this 

 direction may be gauged from a perusal of the Trans- 

 vaal, the Cape, or the South Australian Agricultural 

 Journals ; in South Africa alone a considerable part 

 of Cape Colony, the western halves of the Orange 

 Free State and the Transvaal, the whole of the 

 Bechuanaland Protectorate and a considerable por- 

 tion of southern Rhodesia fall within the "dry lands" 

 area. Some useful practical work may be expected 

 from the newly established dry-land experiment 

 station, but that will onlv intensify the necessity for a 

 scientific studv of the problem. 



There is also need of work bv the plant physiologist 

 on the effect of insufficient water supply on plant 

 growth. In Dr. Leather's paper data are given 

 showing how much water is transpired by a plant in 

 the production of one pound of dry matter, and on 

 the basis of these figures a table is made out showing 

 how much irrigation or rain water is needed to obtain 

 crops of certain sizes. The values depend on the 

 amount of food-stuff available ; less water is needed 

 per pound of dry matter produced in a rich soil than 

 in a poor one. Although there is no direct causal 

 relationship between transpiration and assimilation, 

 the ratios obtained bv different observers in various 

 parts of the world are roughly of the same order ; thus 

 for barley the number of pounds of water transpired 

 per pound of dry matter produced are : — 



Lawes and Gilbert (Rothamsted, 1850) 257 



Wollny 774 



King (Wisconsin, 1894) 30-? 



Leather (Pusa, 1910) on manured soil 480 



,, ,, on unmanured soil ... ... 680 



E. J. Russell. 

 NO. 2143, VOL. 85] 



IHE CAVENDISH LABORATORY. 



'T'HERE is no more pleasant way of spending a 



-*- week-end than by re-visiting the University 

 Town of Cambridge in term time to meet the old 

 friends and comrades of years gone by, and it was 

 a happy thought that induced the writer of the " His- 

 tory of the Cavendish Laboratory " to choose a 

 Saturday for presenting an edition de luxe of the 

 book to the Cavendish Professor of Experimental 

 Physics. 



Saturday, November 12, was a red letter day for all 

 who are interested in the Cavendish Laboratory, for 

 it was the occasion of the assembling of a number of 

 distinguished persons to do honour to the "boy pro- 

 fessor " of a quarter of a century ago, who has so 

 amply justified the confidence of the Board of electors 

 in appointing so young a man to a post of such 

 importance. Clerk Maxwell and Rayleigh were not 

 easy men to follow ; the standard they had set was a 

 high one, the Cavendish Laboratory had become a 

 prominent institution dependent for maintaining its 

 position and for its further development not only on 

 the scientific reputation of its Director, but on 

 his power to attract the ablest j'oung men of the 

 day. 



How far Sir J. J. Thomson has done this was 

 evidenced by the number of distinguished visitors to 

 Saturday's ceremony, among whom we noted : Lady 

 Thomson and her little daughter Joan, Mrs. Sidgwick, 

 the Vice-Chancellor, the Bishop of Ely, the President 

 of Oueens' and many Masters of Colleges, Sir T. 

 Clifford Allbutt, Sir Robert Ball, Profs. P. V. Bevan, 

 R. H. Biffen, F. C. Burkitt, Sir George Darwin, 

 Prof. Ewing, Dr. Wm, Garnett, Profs. W. M. Hicks, 

 F. G. Hopkins, B. Hopkinson, Dr. J. N. Keynes, Sir 

 Joseph Larmor, Profs. Liveing, Leahy, Alexander 

 Macalister, Dr. J. E. Marr, Profs. H.' F. Newall. 

 W. J. Pope, J. H. Poynting, E. Rutherford, Dr. J. E. 

 Sandvs, Mr. Sidney Skinner, the Hon. R. J. Strutt- 

 Mr. H. M. Tavlor, Mr. W. C. D. Whetham, Prof 

 L. R. Wilberf6rce, Mr. C. T. R. Wilson, Prof. G. 

 Sims Woodhead, and Prof. A. M. Worthington. 



In the unavoidable absence of the Chancellor, the 

 Vice-Chancellor presided, and declared his position 

 a sinecure in that the speakers needed no intro- 

 duction. 



Dr. Glazebrook, in making the presentation, began 

 by reading a message, contained in a letter to him- 

 self, from Lord Rayleigh, Chancellor of the Univer- 

 sity : — 



My interest in the Cavendish Laboratory began with — 

 indeed preceded — its inception, and I had the privilege of 

 the acquaintance of that great genius, the first professor, 

 on whom fell, of course, a vast amount of work in con- 

 nection with the building and equipment. The laboratory 

 had hardly more than got to work when British science 

 sustained an irreparable loss by the death of Maxwell. 

 My interest then became a responsibility. During the five 

 years from 1879 to 1884 the educational work was greatly 

 developed under yourself and Dr. Shaw, and in research 

 some good work was done. But I must not dwell upon 

 what, no doubt, most of the present students look upon 

 as the dark ages. For six-and-tvventy years Sir Joseph 

 Thomson has had the direction, and under him the 

 Cavendish Laboratory has assumed the first place among 

 physical laboratories. By his own researches, pursued 

 with astonishing ardour and success, he has opened up a 

 new world, and, what is in some respects a task even 

 more difficult, he has inspired and trained a number of 

 followers, among whom I am pleased to reckon my own 

 son. Cambridge has every right to be proud of the 

 Cavendish Laboratory, its professor, and his staff. 



I will ask you to convey my congratulations to Sir 

 J. J. Thomson. For the future one can wish nothing 

 better than that it should resemble the past. 



