November 5, 1908] 



NATURE 



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 o/ Nature. 



Anomalous Dispersion of Luminous Hydrogen. 



Os pp. 413 and 607 of vol. Ixxvii., and p. 55 of 

 vol. Ixxviii., of Nature, Prof. Schott and Mr. Norman 

 Campbell discuss the question of " The Theory of Disper- 

 sion and Spectrum Scries." Though not desirous of re- 

 opening this discussion, we think the readers of Nature 

 may take some interest in the results of experiments we 

 have just finished upon the anomalous dispersion of 

 luminous hydrogen. 



We used the continuous spectrum given by a narrow 

 capillary tube when filled with hydrogen at nearly atmo- 

 spheric pressure, and traversed by a convenient current 

 given by a large induction coil. In that spectrum we 

 generated horizontal interference fringes by using a Jamin 

 interferential refractor (cf. L. Puccianti, Nuovo Cim., ii., 

 p. 257, 1901), and we sent one of the two rays between 

 the Jamin mirrors through a Geissler tube filled with 

 hydrogen of about 4 mm. pressure. 



When this tube is put in series with the capillary tube 

 above mentioned, the interference fringes at both sides close 

 to the red hydrogen line (Ha) suddenly change their direc- 

 tion, as in the accompanying figure, showing directly tne 



anomalous course of the refractive index near the " absorp- 

 tion line." By measuring the maximum variation of the 

 refractive index (8xio-') and the breadth of the Ha line 

 (2-3 A) we find, according to the Drude-Voigt theory of 

 dispersion (cf. W. Voigt, "Magneto u. Electro-optik," 

 p. 114, 1908), that the ratio of the number of "electrons 

 of dispersion " to that of molecules of hydrogen is only 

 about I to 50,000, and that the damping-constant (cf. Voigt), 

 measured in wave-lengths, is of the order 2-3 .'\ngstr6m 

 units. 



Wo have not succeeded in detecting anomalous dis- 

 persion at the other hydrogen lines, which is expected 

 to be much smaller than that at the Ha line, on account of 

 the smaller absorption (cf. R. Ladenburg, Vcrh. d. deutschen 

 phys. Gcs., X., p. 550, 1908). 



We conclude that our experiments show that it is not 

 possible to explain the dispersion of luminous hydrogen by 

 the existence of one class of electrons only as in the case 

 of non-luminous hydrogen ; we have to introduce new 

 "electrons of dispersion," and the frequencies of these 

 seem to be those of the lines of the so-called first series of 

 hydrogen. 



Rudolf Ladexbirg. 

 Stanislaw Loria. 



Physical Laboratory, University of Breslau, 

 October 17. 



NO. 2036, VOL. 79] 



The 479 Period of Sun-spot Activity. 



In Nature of August 13 (p. 351) the photograph is 

 published of two groups of sun-spots taken on ."August 6, 

 and attention is directed to the remarkable fact that such 

 an outbreak should occur two years after the sun-spot 

 maximum. This renewed sun-spot activity is connected 

 with the 479 period, which I have shown to have been 

 quite persistent — even more so than the eleven-year period 

 — since sun-spots were first systematically observed. In a 

 paper published in the Philosophical Transactions for 190b 

 I gave the times of maxima of this period as being 

 i903-72-)-4-79 n. This would bring the maximum to 

 1908-51, or to about July i of the present year. A 

 retardation of one month in a period of more than four 

 years' duration is, of course, insignificant. 



Simla, October 19. Arthur Schuster. 



Memory in the Germ Plasm. 



Dr. Archdall Reid repeats (Nature, October 15, p. 

 605) his well-known opinion that from infancy forwards 

 a man develops physically and mentally, principally under 

 the stimulus of use, and he adds, " the muscles of an 

 infant's limbs do not grow unless used. His mind is 

 almost blank at birth, but grows under the influence of 

 experience (use). In this way he learns to coordinate his 

 muscles, and a vast deal more." 



There are no italics in the original, but it is to these 

 two statements that I desire to direct attention. 



In regard to the first of them, we may well ask what 

 evidence Dr. Reid can adduce for such a statement. It 

 would be nothing but a vague and even false analogy 

 if he relies upon what happens when limbs are paralysed 

 owing to damage to the spinal cord. Physiologists gener- 

 ally would surely believe that the muscles of an infant 

 tend to grow after birth, just as its bones tend to grow 

 — those of the skull, for instance — quite irrespective of 

 use, however much the process may in some cases be 

 accelerated by use. 



Then, again, there are crucial facts to show that in 

 regard to many most complicated movements it is not 

 necessary for a child to " learn to coordinate his muscles." 

 On the contrary, the possibility of coordinating very many 

 muscles, even for such very complex acts as speaking and 

 wallcing, is brought about as a result of the inheritance 

 of cell and fibre groupings in the brain and spinal cord 

 which only become perfected after birth. It is true that 

 for both these complex muscular acts it commonly happens 

 that trials and failures are made while the nerve 

 mechanisms are developing — hence children may seem to 

 acquire these accomplishments solely as a result of experi- 

 ence. But the real all-important share of inheritance in 

 bringing about the possibility of performing the complex 

 muscular acts in question is conclusively shown by cases 

 in which, from some cause, speech or the ability to walk 

 is delayed to a comparatively late period — when the related 

 nervous mechanisms have had time to become developed. 

 Then, under the influence of some strong excitement, a 

 child who has never spoken a word up to two or even 

 five years (but whose sense of hearing is good) may 

 suddenly begin to speak clearly without antecedent attempts 

 of any kind. Cases of this sort may be found recorded in 

 my work " Aphasia and other Speech Defects " (pp. 5-8). 



The same kind of thing may occur in regard to walk- 

 ing. When mentioning the cases of untaught speech above 

 referred to one day to the late Sir Richard Quain, he told 

 me that one of his children, up to the age of two years, 

 " had not walked a step, or even tried to walk, when one 

 day he put her down in the standing position, and to his 

 great surprise, as well as to that of the nurse, she walked 

 from one side of the room to the other." This also was 

 an untaught act, as there had been no previous trials and 

 failures " (" Brain as an Organ of Mind," p. 607). 



Thus, because insects and many other animals, as Dr. 

 Reid says, " come into the world fully equipped physically 

 and mentally to cope with their environment," and man 

 does not, it does not at all follow that the inherited 

 formative tendencies of man may not go on to a con- 

 siderable extent after birth, even though use, in the 

 majority of cases, does come in as a cooperating cause 



