15^ 



NA TURE 



[April 7, 1910 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



The Term "Padian" in Trigonoiretry, 



From a recently published part of the " New English 

 Dictionary " it is to be inferred that the first authority 

 for the use of the word " radian " was the " Treatise on 

 Natural Philosophy " of Thomson and Tait, the date given 

 being 1879 — that is to say, the date of the new edition 

 of part i. of vol. i. As the word has at least ten years 

 of previous history, it may be desirable to put on record 

 a few additional facts in regard to it. My own first use 

 of it was in class-teaching in the College Hall at St. 

 Andrews in i86g, and I possess a note-book, belonging to 

 one of my students of that year, in which the word is 

 used. The introduction of it was almost simultaneous 

 with my proposal of the word " therm " in connection 

 with the measurement of heat. 



The advantages of the latter word I went so far as to 

 point out in a letter to Nature dated almost exactly forty 

 years ago (see vol. i., p. 606). At that time I was in- 

 clined to suggest the form " rad " in preference to 

 "radial" or "radian," it being advantageous to have a 

 monosyllable for the fundamental unit of a series if 

 auxiliary units like " kilotherm," " millirad," &c., were 

 likely to be called for (see Nature, vol. iii., p. 426). 



It was in 1874, after several conversations on this and 

 similar subjects with the late Prof. James Thomson, of 

 Glasgow, and especially after an exchange, of letters with 

 the late Alexander J. Ellis, that the form "radian" was 

 definitely adopted by me. In that year I came across the 

 following passage in an interesting historico-biographical 

 note ^written by Ellis as an appendix to his " Algebra 

 Identified with Geometry " (London, 1874) : — " Let' u be 

 a unit-line, then, if r and f be both real numbers, rei'if. 

 represents a line of the length ru and inclined to m at 

 f radial angles " (p. 82), there being added in brackets the 

 definition " 2ir radial angles = 4 right angles." As a con- 

 sequence I wrote to him, and he declared at once for the 

 form " radian," on the ground that it could be viewed as 

 a contraction for " radt-al an-gle " in accordance . with 

 precedents in chemistry which he had himself followed in 

 his nomenclature of the so-called " stigmatic " geometry. 

 He also incidentally mentioned that he had used the ex- 

 pression "radial angle" from his Cambridge under- 

 graduate days. Thos. Mum. 



Cape Town, South Africa, March 6. 



The Fertilising Influerce of Sunlight. 



The letters on the above subject in Nature of Feb- 

 ruary 17 and March 3 and 10 are of much interest. In 

 many parts of the world artificial heating of the soil is a 

 regular practice. For example, in the rice districts of 

 heavy rainfall in the Bombay Presidency the seed-bed for 

 transplanted rice and some small millets is almost in- 

 variably subjected to a process known in the vernacular as 

 " rab." This consists of spreading a layer of branches, 

 grass, cow-dung, &c., over the surface of the plot (often 

 only a few metres square) selected as the site of the seed- 

 bed. This material is then slowly burnt before the break- 

 ing of the monsoon. 



There is a general agreement as to which kind of 

 " rab " is best, that consisting largely of cow-dung (in the 

 form of a plaster with • chopped straw) being considered 

 by far the best. Then comes that composed of the branches 

 of certain species of Terminalia, after which come those of 

 any available trees, and finally that composed of dried 

 grass. 



. An experiment I conducted on these materials in the 

 year iqo6— 7 at Lanowli, in the rice district above the 

 Ghats between Bombay and Poona, gave the results stated 

 below. Unfortunately, an untimely shower fell a few days 

 before the material was burnt, so that the temperature of 

 the soil was probably not raised so high as in ordinary 

 seasons ; this temperature was taken by scraping off the 



NO. 21 10, VOL. 83I 



ashes at various points and inserting a thermometer 3 or 

 4 centimetres into the soil immediately after burning ; it 

 varied between 200° and 230° F. 



The material was prepared and burnt in the ordinary 

 method used by the natives ; in addition, plots were added, 

 one of which was manured with safilower {Carthamia 

 tinctoria) cake, another with cow-dung, another with ashes 

 scraped off a " rabed " plot, while in a fourth the soil 

 was finely pulverised to a depth of about 8 cm., and in a 

 fifth the surface soil was removed to this depth, placed on 

 iron sheets, and heated from beneath until a temperature 

 of 200° to 230° F. was reached, when it was allowed to 

 cool. 



At the time of transplanting, twenty average seedlings 

 were taken from each of the plots, dried, and weighed. 



The results were as follows : — 



Treatment of plot 



AT anured with safBower cake. 

 " Rabed " with branches of 



Terminalia 



" R abed " w i 1 h m ixed branches 

 Manured wiih ashes of mixed 



branches 



Manured with cow-dung 



" Habed " with cow-dung ... 



Soil pulverised 



Soil heated 



Averase dry weight of seed- 

 lings (in grams) in each of 

 the triplicate plots 



A 



0-4CQ7 



0*0879 



0'2l8l 



0-0797 

 o 0928 

 o'256i 

 o'ogog 

 o*3562 



B 



0-4967 



•(null I 



o"i7o8 



o"io94 

 o 0772 

 o'3i72 

 o"o625 

 o'2g68 



O'lOCO 



o'22;6 



Mean 



o'o879 

 o'i773 



o'o948 



O'oSrO 



0-2866 

 0-0845 



0-2935 



It should be noted that owing to scarcity of this material 

 at the time sufficient branches of Terminalia could not be 

 obtained even for the single plot. Hence, probably, the 

 poor result on this plot. 



From the above it will be seen that the raison d'etre of 

 this process is to obtain the effect of heat, and neither to 

 improve the physical condition of the soil (cf. plots 7 and 8) 

 nor to supply plant food (see plots 4 and 5). The ashes 

 have practically no value, and the natives state that it is 

 of no consequence when the ashes, as is often the case, are 

 removed by wind. 



The enormous effect of safflower cake is well known, 

 an application to sugar-cane being many times more 

 efficient than that of any other cake when applied to give 

 equal quantities of nitrogen. The reason for this is under 

 investigation. 



The fertilising effect of heat on soils has been known for 

 ages, as witness the ancient practice above detailed. That, 

 however, it is due to the causes assigned by Drs. Russell 

 and Hutchinson, viz. a partial sterilisation of the soil, is 

 very much open to doubt. In their extremely interesting 

 work at Rothamsted they find an increase in bacterial 

 activity and rate of increased decomposition of organic 

 matter after partial sterilisation associated with an in- 

 creased crop yield. There is the possibility, however, that 

 these latter phenomena are accompaniments, and not the 

 causes, of the increased crop-yields, all being the result of 

 a destruction of toxic material in the soil. In any case, 

 the theory put forward is apparently incapable of explain- 

 ing many causes of sterility in soil, and is, apparently, not 

 a general explanation that has any practical bearing on 

 the general question of soil fertility. For example, it is 

 difficult to see how it can account for the fact that certain 

 plants will not grow in the immediate neighbourhood of 

 others, as the present writer has found to be the case 

 (" Memoirs of the Department of Agriculture in India," 

 Bot. Ser., vol. xi.. No. 3, April, 1908). 



The excellent work of the Ij.S. Bureau of Soils has 

 proved that roots of plants excrete a toxic substance. The 

 present writer has noted the same phenomenon, and has 

 further isolated the substance from water in which plants 

 have been cultivated. A further paper on this question is 

 in preparation. It may, however, be stated here that if 

 water rendered toxic by the growth in it of plants is shaken 

 with benzene, toluene, chloroform, or carbon bisulphide 

 (the antiseptics used in experiments for partially sterilising 

 soil), this toxic substance is rendered insoluble, and there- 

 fore innocuous. 



As an example, when such water is shaken with 

 toluene, an emulsion is formed which floats on the surface 

 of the water. If this emulsion is poured off and the 

 toluene and water allowed to evaporate, a residue is left 



