8io 



NATURE 



[August 25, 1921 



to think. Compare, as products of these oppK>site 

 types of mental training, Darwin and Huxley with 

 devout Mohammedan and Hindu ecclesiastics. The 

 evidence in favour of scientific education is enormous, 

 decisive, indisputable, but it lies outside the sphere of 

 botany and zoology, in psychology and history. By 

 whatever rational standards we judge human com- 

 munities — material or intellectual progress, efficiency 

 in peace and war, wealth, enterprise, energy, the pro- 

 duction of great thinkers and men of action, civil war, 

 brigandage, murder and other crimes, and so on — we 

 find invariably that the societies the mental training of 

 which has most nearly approached the scientific ideal 

 are the superior. Compare the results of the mental 

 training given by Socrates and his fellows to the 

 ancient Greeks with that given by the Russian popes 

 to their victims. Many nations {e.g. the Romans) 

 have fallen because a change for the worse in mental 

 training left descendants too inefficient to preserve that 

 which better-trained ancestors had secured. Many 

 nations {e.g. after the Reformation) 'Tiave arisen be- 

 cause improved mental training enabled them to sur- 

 pass competitors. Consider the late war and how 

 completely the more biassed peoples have been 

 smashed. But this is a subject too vast for present 

 consideration ; I have tried to deal with it elsewhere.* 

 I may be right or wrong as to the conclusion? I 

 have reached, but clearly the evidence and probleins 

 I have instanced exist. Clearly they are matters for 

 biology, althoug^h they have been neglected by her. 



Academic biology is of little account in the world. 

 The hobby of some naturalists who use not a tittle 

 of the evidence available, she possesses next to no 

 established truth. Her few students are engaged in 

 unending disputes, all of which are consequent on 

 a misuse of words or a neglect of crucial test- 

 ing. Her indefensible terminology separates her 

 from a host of subsidiary sciences. But a biology 

 clarified and simplified by a precise terminology, 

 and in possession of a classification of characters 

 similar to that employed in other studies, might 

 easilv become the queen of sciences. A few wide 

 generalisations accepted by everyone would then re- 

 olace the present chaos of opinions, and provide a 

 basis for work of practical utility. The use of evi- 

 dence from other studies would make their students 

 her own. So strengthened, she would become a power 

 in the land, and perhaps lav the foundations of that 

 golden age of science and human wisdom and well- 

 being of which we all dream. 



Surely there are biologists who perceive that the 

 failure to establish truth can have no cause other 

 than lack of right scientific method, and who are 

 prepared to substitute the method of discussion which 

 has created other sciences for that of controversy 

 which has wrecked biology. 



G. Archdall Reid. 



Magnetic Double Refraction of Smokes. 



The interesting discovery recorded by Sig. Tieri in 

 Nature of August i8, p. 778, that the fumes from an 

 iron arc can, when subjected to the action of a magnetic 

 field, rotate the plane of polarised light, is in close 

 accord with the view of the structure of such fumes 

 advanced by Prof. Elihu Thomson in his recent 

 letters to Nature, and agrees also with the observa- 

 tion of Mr. Speakman and myself (see Nature, 

 June 23, p. 520; and July 14, p. 619). 



Prof. Thomson explains the sudden enhanced 

 luminosity of the light scattered by the iron oxide 

 smoke when the magnetic field is applied by the 

 particles arranging themselves along the lines of 

 force. For this structure to be effective the particles 



^ Vide "Prevention of Venereal Dinease," reviewed in Naturb, April 14. 



NO. 2704, VOL. 107] 



cannot be spherical, but must consist of rods or 

 chains, for only then would the intensity of the re- 

 flected or scattered light vary with " end on " or 

 "length on" incidence. This was confirmed by a 

 microscopic examination of the iron oxide fume, 

 which showed the particles to consist of short strings 

 or chains of roundish beads not touching one another. 



The experience of Mr, Speakman and myself is 

 that the fumes from metallic arcs in air undergo 

 rapid changes with time. The minute particles pro- 

 duced at first by condensation of vapour aggregate 

 together to form complexes, which often show a 

 definite^ chain-like structure when examined after 

 deposition on a slide, but in the air are continually 

 altering their form under molecular bombardment. 



Now it seems likely that if by magnetic or electric 

 forces the small chains or strings can be made to 

 space themselves with their axes all in one direction, 

 not only will the effect described by Prof. Thomson 

 be produced, but a beam of polarised light traversing 

 the fume at right angles to the field of force would 

 suffer rotation provided that the plane of polarisation 

 is neither parallel nor at right angles to the longer 

 axes of the small chains. This is just what Sig. Tieri 

 finds, and it might be expected further, if the above 

 explanation is the correct one, that the magnetic double 

 refraction would vary with the age of the smoke and 

 its method of production. The bluish-coloured smoke 

 found by Prof. Thomson to accompany the yellow 

 fumes from the iron arc, and which did not exhibit 

 the magneto-optical effect, consisted probably of single 

 particles, and would be unlikely to show magnetic 

 double refraction. It corresponds with the initial 

 stage of the oxide clouds we have studied before 

 agglomeration has had time to occur. 



This striking behaviour of iron oxide dispersed in 

 air discovered by Sig. Tieri exhibits a close parallel 

 to the behaviour of the same substance dispersed in 

 water. Cotton and Mouton and others have inves- 

 tigated the magnetic double refraction of iron oxide 

 hydrosol, and they ascribe the effect to the orientation 

 of rod-sha|:)ed or lamellar ultramicrons. Further, the 

 magnitude of the effect was found to increase as the 

 colloid became coarser. 



A continuation of the work commenced by Sig. 

 Tieri may well lead to much interesting information 

 on the form of the particles in smokes. 



R. Whytlaw-Gray. 



Eton College, Windsor, August 21. 



The Contractile Vacuole. 



In connection with previous correspondence on the 

 mode of production of the contractile vacuole in 

 Protozoa (Nature, vol. cvi., pp. 343, 376, 441), I fina 

 that it is, in point of fact, Prof. Marcus Hartog to 

 whom the credit of the osmotic view is to be given. 

 In a communication to the British Association in 

 1888 (Rep., p. 714) this observer pointed out that, 

 owing to the semi-permeable surface membrane, sub- 

 stances in solution in the protoplasm of these 

 organisms must attract water, which accumulates 

 at a particular spot until it reaches the surface, 

 breaks through the membrane, and escapes. The 

 membrane spontaneously closes up as the distension 

 is relieved. Prof. Hartog shows that Tf substances 

 such as sugar or potassium nitrate are dissolved in 

 the outer water to a sufficient osmotic concentration, 

 the production of the vacuole ceases. The paper was 

 reprinted in Ann. Mag. Nat. Hist., Sec. 6, vol. iii., 

 p. 64 (1889). The theory was worked out in more 

 detail by Degen {Bot. Zeit., vol. Ixiii., abt. i, 1905), 

 and is explained by Prof. Hartog in his article on 

 Protozoa in the Cambridge Natural History (1906), 



