October, 1905.J 



KNOWLEDGE & SCIENTIFIC NEWS. 



^43 



nervous centres when a screen, with a luminous base, is 

 used. It is inferred from the experiments : (i) That 

 the sensorial ner\-ous centres are specifically different ; 

 (2) that there is a certain adaptation, not only between 

 physical ag-ents and the sensorial agents destined to 

 receive them, but between those ag'ents and the nervous 

 centres which perceive them after reception by the sen- 

 sorial agent ; (3) that there are certain common pro- 

 perties implying analogy of nature, between sensorial 

 excitants and the peripheral or central nervous 

 organs destined for their perception, since they show, 

 by the sort of specific resonance referred to, analogous 

 emissive properties. 



The existence of X' rays first noticed by M.'Blondlet, 

 and referred to above, seemed to be confirmed by M. 

 Charpentier, v.ho published an account of some obser- 

 vations of his own, which showed that N' rays exert a 

 physiological action which is the inverse of that of the 

 N-rays. Thus, they cause a decrease of the sense of 

 smell, instead of increasing it. as do the X-rays. 



The contributions to the study of the X-rays, and the 

 still more mysterious N' rays form, indeed, in France, 

 a complete literature bv itself. Perhaps nothing quite 

 so extraordinary- has previously been made known. 



A very noteworthy fact, however, is this, that numer- 

 ous practised obsersers, including some of the most 

 eminent scientific men of the day, have been quite 

 unable to observe the effects of these X-rays, even 

 when looking for them under conditions identical with 

 those under which they were recorded by the obser\-ers 

 in France. 



We have thus next to notice some ven,- important 

 criticisms upon the whole series of published facts, and 

 especially is it necessan.- to consider the remarks of 

 Dr. Lummer, the German physicist, who commented 

 upon M. Blondlot's researches in a paper read before 

 the German Physical Society in Xovember, 1903. 



Dr. Lummer, without wishing, in the meantime, to 

 ous practised observers, including some of the most 

 that a whole series of Blondlot's researches may be 

 almost completely imitated without using any source of 

 radiation, and that the changes in form, brightness, 

 and colour of the surfaces obser\-ed by Blondlot may be 

 explained by what goes on in the eye itself, and by the 

 competition between the rods and cones of the retina 

 in vision in the dark. Kries explained the function of 

 the cones as being our apparatus for brightness fit for 

 distinguishing colour, and the rods as blind to colour, 

 and forming our apparatus adapted for darkness. Be 

 fore the cones perceive coloured light, the rods produce 

 in the brain tlie impression of colourless brightness. 

 The fovea centralis contains cones only, while the rods 

 predominate at the periphery of the retina. Thus, in 

 direct vision (foveal') the rods are excluded, and only 

 come into action in indirect (periphcnil) vision. With 

 small brightness these two portions of the visual ap- 

 paratus come into sharp contest, and if the dimness is 

 great, the colour-blind rods prevail, and everything ap- 

 pears grey. Dr. Lummer. in his work on " The grey 

 glow and the red glow," explains on this theor\- the 

 sudden chattg'es which occur when a body is obser\"ed 

 in a dark room, and its temperature steadily raised. 

 The sudden change from dark to grey, and, again, the 

 sudden increase from the grey glow to the red glow, 

 are due to the successive stimulation, first, of the retinal 

 lods, .and then of the retinal cones. Shadow^' vision 

 i? produced when the fovea centralis is not stimulated, 

 and n sheet of heated platinum, for example, observed 

 in the dark. A source of radiation is perceived, but not 

 c'early seen, till the cones also are stimulated, which 



occurs at ab«}ut 500° C. In some of Blondlot's experi- 

 ments the case of the shadowy vision thus described 

 .•■eenis io be reproduced, and the effect has been shown 

 to an audience. .\ dull, glowing platinum plate is first 

 seen by extra foveal parts of the retina. On interpos- 

 ing the hand or .a lead screen, the gaze is limited and 

 fixed, the foveal part of the retina is brought to bear, 

 and the actior, of the rods excluded. The tesult is that 

 the plate appears less bright and more red-coloured. 

 Time and eft'ort are .-equired for this change, as in tlie 

 exoeriments described by Blondlot. The phenomena 

 are thus probably subjective to a large degree, or may 

 be described as due to objective occurrences in the 

 retina. 



.\n e> tended series of observations were made in the 

 physiological laborator]i- of the L'niversity of Glasgow 

 with the object of confirming Blondlot's observations, 

 but the results were uniformly negative. Prof. 

 McKendrick and Mr. Colquhoun describe their experi- 

 .ments, which were carried out with the help of seven 

 observers who were trained to accujate work. On ob- 

 serving a small fluorescent screen in the dark these ob- 

 servers noticed apparent changes of brightness when 

 there was no contraction of muscle, and no question of 

 X-rays reaching the fluorescent patch. When the ob- 

 servers were asked to look into the distance beyond the 

 bright spot, and report on the brightness of the screens, 

 the result was very noteworthy. TTiey all reported, 

 without exception, that the brightness of the screens 

 was constant, and that muscular contraction made no 

 difference. In this case the accommodation of the eyes 

 for near vision was relaxed. It is suggested that there 

 is a difficult}- in accommodating for the fluorescent 

 circle observed, and that there is a wavering movement 

 of the cilian.- muscles, and, perhaps, also a wavering in 

 the size of the pupils. Besides this, it should be noticed 

 that Heinrich, some time ago, found that the pupil 

 dilates when examining an object situated in the field 

 of indirect vision, and that it dilates still more during 

 a short mental effort. He found also that, on direct- 

 ing attention to an object in the field of indirect vision, 

 the ciliary mu.scle relaxes, thus diminishing the curva- 

 ture of the crystalline lens, and this change is very 

 marked during mental calculation. Prof. McKendrick 

 suggests that the mental condition of some observers in 

 a state of expectancy may react on the intrinsic 

 muscles of their eyes, and thus they may see what they 

 think they should see. 



Prof. K. W. \\'ood, of -America, when on a visit to 

 Europe in the autumn of last year, spent some time in 

 examining the methods of obtaining the X-rays in one 

 of tlie laboratories on the Continent, where the mani- 

 festations of the new rays were announced as verv dis- 

 tinct. He failed, however, in obtaining anv evidence 

 which satisfied him that these rays really existed. 

 .\fter spending some hours in watching" and taking 

 part in all the various experiments by which the pro- 

 perties of the X-rays are supposed to be indicated, he 

 left the laboratory with the firm conviction that the 

 few observers who have obtained positive results have 

 been in some way deluded. The interposition of the 

 hand in the path of the rays seemed to make no differ- 

 ence in the brilliance of a small electric spark, which 

 was supposed to be acted upon by these ravs, though, 

 according to M. Blondlot, the cutting- off from the 

 spark of the X-rays which takes place when the hand is 

 interposed makes a distinct difference in its brightness. 



Prof. ^Vood regards the photc^raphic method 01 

 showing an objective effect due to the rays to be quite 

 illusory. The effects of refraction bv an aluminium 



