158 



NA TURE 



[August 5, 1909 



strenuous race of men. The author's particular 'text 

 is the function of the State in fostering agriculture; 

 left to himself, the farmer is normally a strong in- 

 dividualist, -who readily becomes isolated and hide- 

 bound. His sole chance of success in modern life is 

 collective action, and Prof. Bailey discusses in suc- 

 cessive chapters the extent to which the State can 

 profitablv intervene in the organisation of rural life by 

 education and by starting various forms of cooperative 

 work which will lead the farming community to act 

 together. Different as the agricultural conditions are 

 in this country and in America, the problems are the 

 same in both places, and Prof. Bailey's discussion of 

 the subject gains a special interest for us at this 

 moment, when the Chancellor of the Exchequer has 

 just set aside a " development grant " to be devoted 

 to the promotion of all agencies for encouraging rural 

 life. 



The Problem of flic Fcchlc-miiidcd. An Abstract of 

 the Report of the Royal Commission on the Care 

 and Control of the Feeble-minded. With an intro- 

 duction by Sir Edward Fry, G.C.B. Pp. x+113. 

 (London : P. S. King and Son, 1909.) Price is. net. 



The appearance of this abstract is most opportune. 

 The small committee of persons interested in social 

 problems which is responsible for its publication is 

 anxious to bring before as large a section of the public 

 as possible the urgency of the matters in question, and 

 points out in the preface of the book that the Poor 

 Law Commissioners have given it as their opinion 

 that if the recommendations of the Commission on 

 the Care of the Feeble-minded were carried into 

 effect, a svstem of control over the feeble-minded 

 would be initiated which would free the Poor Law 

 administration from one of its greatest ditTiculties 

 and, we may add, the country from a cause of 

 enormous expenditure. In his introduction Sir 

 Edward Fry quotes Bagchot's sad reflections upon 

 the undue haste and benevolent thoughtlessness with 

 which so much philanthropic effort is attended, and 

 the terrible question w'hich he poses as to whether 

 the benevolence of mankind does not do more 

 harm than good. Sir Edward Fry can, however, re- 

 commend the work of the Commission on the Feeble- 

 minded as one done with deliberation and not with 

 " a wild passion for instant action." The various 

 problems which came before the Commission, such as 

 mental defect and drink, mental defect and crime, and 

 mental defect and illegitimacy, are adequately epi- 

 tomised, and the far-reaching recommendations of the 

 Commission duly considered as to the essential points. 

 The book also contains some special articles, of which 

 that upon segregation, by Mr. Galton, we can espe- 

 cially recommend to our readers. 



The Economy and Training of Memory. By Henry J. 

 Watt. Pp. viii+i2S. (London: Edward Arnold, 

 igog.) Price is. 6d. net. 



The training of the memory is undoubtedly a part of 

 any good education, and it has hitherto been too much 

 the peculiar field of the faddist and of ingenious but 

 ignorant a priori system-makers. This little book, 

 which aims at making of practical value to student 

 and teacher the results of scientific experiment into 

 the subject, is therefore to be welcomed. It is true 

 that some of its precepts appear obvious, but where 

 there are so many conflicting truisms the selection of 

 the right obvious is not unimportant; and much de- 

 finite information is given on particular points where 

 the merely empirical adviser is quite at a loss, e.g. 

 the advantages and disadvantages of specific types of 

 mental imagery, and the variations of method corre- 

 sponding to differences in the material to be memor- 



NO. 2075, VOL. 81] 



ised. Moreover, if the book did no more than free 

 the ordinary adult from that excessive distrust of his 

 memorv, which is so bad in effect, and is, perhaps, too 

 optimistically believed by Mr. Watt to be quite un- 

 grounded in fact, it would be abundantly justified. 



Mr. W'att considers the mechanical memory of asso- 

 ciation to be, in a sense, more fundamental than the 

 intelligent memory based on connection of thought, 

 since the association between w-ord and " meaning " 

 is in itself mechanical. It seems doubtful if that ulti- 

 mate " association " of meaning and imagery can be 

 expressed so simply ; but the point, though of great 

 interest, is of minor importance in a confessedly prac- 

 tical book. 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can lie undertake 

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

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications.] 



Rate of Helium Production from the Complete Series 

 of Uranium Products. 



.A KNOWLEDGE of this constant is essential to the estima- 

 tion of the ages of minerals from their helium content. In 

 a paper published in Proc. Roy. Soc, July 28, 190S, I gave 

 the ages of some minerals provisionally on the assumption 

 that the rate was 913X10-* c.c. per gram U3O, per 

 annum. This rate was calculated from Rutherford's in- 

 direct data. It has received much support from Sir J. 

 Dewar's determination of the rate of production by radium 

 with its immediate products. I am now in a position to 

 confirm it further by an experiment on the rate of growth 

 of helium in a solution of pitchblende ; I speak of a solu- 

 tion, but it has been found impracticable to take up all 

 the constituents by one solvent. Two solutions were 

 necessary. 



The pitchblende solutions contained 115 grams of U,0,, 

 and yielded in sixty-one days a quantity of helium which 

 was measured as 2x10-° c.c. in the capillary of a McLeod 

 gauge. This gives the rate as 10-4x10-' c.c. per gram 

 U,0„ per annum. No stress can be laid on the close 

 agreement with Rutherford's estimate in view of the very 

 small gas volume measured. The experiment proves, how- 

 ever, that that estimate is of the right order of magni- 

 tude. Larger scale experiments are in progress, and 

 these, in conjunction with similar experiments on 

 thorianite, will, it is hoped, enable data on the quantity 

 of helium in minerals to be translated into estimates of 

 lime with full confidence. R. J. Strutt. 



Imperial College of Science, South Kensington, 

 July 27. 



A Kinematic Illusion. 



People are sometimes amazed by noticing that in a 

 motor-car seen through railings the wheels appear to 

 revolve the wrong way. As the eye follows the moving 

 objects it is convenient to imagine that the car, which 

 mav be actually running to the right, is stationary, while 

 a vertical rail is moving past it to the left with an equal 

 velocity. The apparent intersection of this rail wdth the 

 upper edge of the wheel is a point running round in a 

 contrary direction to that of the rotation of the wheel. 

 This moving point suggests rotation of the wheel. When 

 oblique lines swing in front of vertical lines the move- 

 ment of the intersections is curious to watch. It is true 

 that the lower half of the wheel goes against our theory, 

 but at a given moment its effect may be less noticeable, 

 either from being hidden in dust or because the eye has 

 a very small range of close attention. I have seen the 

 appearance, and have had reports of it from others, but 

 cannot speak with precision as to the condition of seeing 

 it effectively. 



It is common to rotate vacuum tubes while a discon- 

 tinuous spark illumines them. A spark may pass at the 

 instant of starting one revolution, and the illumination 



