June 29, 1905] 



NA TURE 



195 



THE "N" RAYS. 



A Collection of Papers communicated to the Academy 

 of Sciences, with Additional Notes and Instructions 

 for the Construction of Phosphorescent Screens. 

 Bv Prof. R. Biondlot. Translated by J. Garcin. 

 Pp. xli + 8j. (London: Longmans, Grcon and Co., 

 1905.) Price 3^. 6d. net. 



THi"" ji-rays, so called because the first 

 •innouncement of their e.xistence came from 

 .\a]u\ , have attracted the attention of physicists and 

 physiologists all over the world; but the peculiarity 

 about them is that the phenomena said to be pro- 

 duced bv these rays when they fall on a slighlly 

 lluorescing screen have been observed chiefly in France 

 bv Prof. Biondlot and others of his school, while 

 manv experienced observers in Germany, America, 

 ;uid England have wholly failed to obtain a satis- 

 liciory demonstration even of their existence. The 

 iiason is that the so-called proof of their existence 

 depends, not on objective phenomena that can be 

 critically examined, but on a subjective impression on 

 the mind of the experimenter, who sees, or imagines 

 he sees, or imagines he does not see, a slight change 

 in the degree of luminosity of a phosphorescing 

 screen. It is true that, more than once, a photo- 

 graph has been taken of such a screen supposed to 

 be unaffected and contrasted with a photograph of 

 the same screen when it was supposed to be affected 

 by the ravs, with the result that the patch of luminous 

 surface appears to be a little brighter in the latter 

 case than in the former. Even this photographic 

 evidence, however, is unsatisfactory, as a slight differ- 

 ence in the time of exposure or in the method of 

 development would readily account for the apparent 

 contrast. 



Yet, in this little book, we have a reprint of Prof. 

 Blondlot's original papers, in which experimental 

 evidence is adduced, with a wonderful appearance of 

 accuracy in detail, of the polarisation of the rays, of 

 their dispersion, of their wave-length, and of other 

 physical phenomena attributed to them. Prof. Blond- 

 lot's experiments are well contrived, and they give 

 every appearance of being arrangements by which 

 accurate data should be obtained ; but in every 

 case the ultimate test is the subjective one made on 

 the mind of the observer as to whether a spot 

 of slightly phosphorescent surface becomes more 

 luminous or not. The n-rays, according to Prof. 

 Biondlot, are a new species of light, light, however, 

 which only affects the retina with the aid of a fluor- 

 escent substance. They traverse many metals, black 

 paper, wood, &c. They cannot pass through sheet 

 lead, but thev pass readily through aluminium. They 

 influence not only a fluorescent substance, but the 

 spark of an induction coil. They can be reflected 

 from a polished glass surface or from a plate of 

 polished silver. They have a kinship with well known 

 radiations of a large wave-length. They exist in 

 solar rays. Produced from an Auer burner they can 

 be focu.sed by a quartz lens ; the lens itself may even 

 become a source of ii-rays. 



Calcium sulphide can store up the rays, while 



NO. 1 86 1, VOL. 72] 



aluminium, wood, dry or wet paper cannot do so. 

 Ordinary light, when it falls on the retina, causes a 

 more luminous sensation when accompanied by 

 11-rays. Bits of wood, glass, rubber, &c., emit 

 the rays when compressed. Bodies in molecular 

 strain, like Rupert's drops, hardened steel, &c., emit 

 the ravs. An old knife, found in a Gallo-Roman 

 tomb, equally with a new knife, sends out rays. 

 There are other rays also, which must be called 

 ;i,-rays, which are emitted from a Nernst lamp. These 

 diminish the glow of an induction spark. Ethylic 

 ether, " when brought to a state of forced extension," 

 emits the Hj-rays, &c. 



To see all these wonderful phenomena the eye must 

 be not only kept in the dark for a considerable time, 

 but it must be specially trained. A. Broca states that 

 in his own case it required practice for six weeks 

 before he could see the effect of the rays. The eye 

 must be adapted not only to darkness, but to very 

 feeble light. The mind must be free, so as to con- 

 centrate itself on the observation to be made. These 

 seem to be admirable arrangements for obtaining an 

 illusive subjective impression ! It is said that MM. 

 d'Arsonval and Mascart have also observed some of 

 the phenomena. Many other French observers, with 

 less weighty names, have al.so been cited as witnesses. 

 The general body of men of science are doubtful, as 

 they cannot receive evidence of such a strangely sub- 

 jective character, while not a few, and the writer 

 places himself in this category, are of opinion that 

 while they do not for a moment reflect on the bona 

 fides of the French observers, they hold that these 

 observers have been the subjects either of an illusion 

 of the senses or a delusion of the mind. 



John G. McKendrick. 



THE SCIENCE OF EDUCATION. 

 School Teaching and School Reform. By Sir Oliver 

 Lodge. Pp. viii+171. (London: Williams and 

 Norgate, 1905.) Price 35. 



T"HE science of eduftttion is as yet rudimentary and 

 ill-defined. So little has it developed, indeed, that 

 many schoolmasters deny its existence. An art of educa- 

 tion they recognise, and that they claim to practise. 

 Teachers, it is urged, are born, not inade, and pro- 

 fessional training is useless. Yet it is the possibility 

 of the future existence of a complete science of educa- 

 tion which is the inspiring belief of the best modern 

 educators. These teachers are now approaching the 

 problems of the class-room and the difficulties of 

 school organisation as subjects for investigation and 

 experiment by scientific methods, and there is every 

 reason for hopefulness in the results which have been 

 obtained in recent years. 



The formulation of the fundamental principles of a 

 complete science of education will probably be the 

 work of some great educationist as yet unborn, who 

 will be able from the educational material at his 

 command to extract the essentials and to weave them 

 into living generalisations round which the science 

 will crxstallise into an orderly and harmonious whole 

 To the elucidation of such a science many workers 



