2 5 6 



NA TURE 



I J an. 15. 1880 



am standing a little on one side. 'J bej go away in ih 

 so that 100 is the farthest number I tan ; ee distinctly. It i b 

 dusky grey, and paler near to me ; up to 20 it occupies a dispro- 

 portionate size. There are sorts of woolly lumps at the tens. 

 These pictures are not of such frequmt occurrence in my mind 

 as formerly. The practice of working arithmetic has rather 

 expelled them. 



Since the foregoing remarks were first sent to the 

 printer, many additional cases have reached me, which I 

 regret to have no space left to include. One very in- 

 teresting group consists of three cousins and the daughter 

 of one of them. Another case was brought to my notice 

 by a correspondent ; it was published in the Atlantic 

 Monthly, February, 1873, p. 199, with an accompanying 

 diagram, and is signed by Miss H. R. Hudson. I have 

 little doubt that many allusions to the faculty of visualising 

 numerals in diagrammatic and coloured shapes might be 

 found to exist scattered here and there in various books. 



Of the many results to be drawn from the foregoing 

 extracts, I do not at present care to dwell upon more 

 than these. In the first place I am sure that all will 

 agree with me in saying that the descriptions bear 

 evident marks of careful and trustworthy observation. 

 In the second place, although they refer to characteristics 

 which the majority of my readers may not possess, their 

 language is sufficiently clear to convey a good idea of 

 what is meant to be conveyed. In the third place, these 

 independent statements powerfully corroborate and ex- 

 plain one another. Therefore, although philosophers 

 may have written to show the impossibility of our discover- 

 ing what goes on in the minds of others, I maintain an 

 opposite opinion. I do not see why the report of a 

 person upon his own mind should not be as intelligible 

 and trustworthy as that of a traveller upon a new country, 

 whose landscapes and inhabitants are of a different type 

 to any which we ourselves have seen. It appears to me 

 that inquiries into the mental constitution of other people 

 is a most fertile field for exploration, especially as there is 

 so much in the facts adduced here, as well as elsewhere, 

 to show that original differences in mental constitution 

 are permanent, being little modified by the accidents of 

 education, and that they are strongly hereditary. 



I trust, therefore, that the publication of this memoir 

 may prove to be the means of inducing some persons to 

 furnish me with information of the kind I am now seeking. 

 I want to hear of well-marked and properly-authenticated 

 instances of persons who are able to recall, or represent to 

 their imagination, with great vividness, either sights, 

 sounds, smells, or tastes, and to obtain information that 

 may throw light on the peculiarities of the representative 

 faculty in different families and races. 



Francis Galton 



42, Rutland Gate, London 



ON A MODE OF EXPLAINING THE TRANS- 

 VERSE VIBRATIONS OF LIGHT 

 THERE has been considerable difficulty in arriving at 

 a satisfactory conception of the means by which the 

 transverse vibrations of light are produced in the ether. 

 In the attempt to surmount this difficulty some have gone 

 so far as to conjecture that this structure of the ether 

 must resemble that of a solid; for it was imagined that 

 nothing but such a structure could propagate transverse 

 vibrations. Yet the supposition of the ether being any- 

 thing like a solid appears to be in direct antagonism to the 

 evidence of our senses ; for we move about so freely in 

 this "solid" as to be unconscious even of its existence. 



My object here is to direct attention more especially to 

 a suggestion thrown out by the late Prof. Clerk Maxwell 

 in regard to this point. This suggestion is contained in 

 the article, " Ether," in the new edition of the " Encyclo- 

 paedia Britannica,"in connection with a notice of a theory 

 of the constitution of the ether (considered in special 



relation to the problem of gravitation) by the present 

 writer, and published in the Philosophical Magazine for 

 September and November, 1877, and February, 1878. 

 After referring to the fact that the present writer " has 

 supposed that the ether is like a gas whose molecules 

 very rarely interfere with each other, so that their mean 

 path is far greater than any planetary distances," Prof. 

 Maxwell continues as follows : — 



" He has not investigated the properties of such a 

 medium with any degree of completeness, but it is easy 

 to see that we might form a theory in which the mole- 

 cules ' [atoms of ether] never interfere with each other's 

 motion of translation, but travel in all directions with the 

 velocity of light ; and if we further suppose that vibrating 

 bodies have the power of impressing on these atoms of 

 ether some vector property (such as rotation about an 

 axis) which does not interfere with their motion of trans- 

 lation, and which is then carried along by the atoms of 

 ether, and if the alternation of the average value of this 

 vector for all the atoms of ether within an element of 

 volume be the process which we call light, then the equa- 

 tions which express this average will be of the same form 

 as that which expresses the displacement in the ordinary 

 theory." 



There is one point in the above suggestion I would 

 briefly remark upon, viz., the supposition made by Prof. 

 Maxwell that the atoms of ether " never interfere with each 

 other's motion of translation " [i.e., never encounter each 

 other]. This supposition seems to have been called for 

 by the fact previously mentioned in the same article 

 ("Encyc. Brit.," p. 572), viz., that "the ether transmits 

 transverse vibrations to very great distances without 

 sensible loss of energy by dissipation," whereas it is con- 

 tended that if the ether atoms encountered each other 

 (frequently at least), " the energy of the regular vibra- 

 tions would be frittered away into that of the irregular 

 agitation which we call heat." But I would venture to 

 suggest that, as we have no proof that no dissipation 

 whatever of the energy of light takes place in long dis- 

 tances (but perhaps even some indication to the contrary), 

 it would appear evident that no necessity really exists for 

 supposing that the atoms of ether never interfere with 

 each other's motion of translation. I think it will be 

 admitted as a reasonable conclusion that so long as the 

 dissipation of the energy (of the light) attendant on the 

 mutual encounters of the ether atoms is no greater than 

 observation allows us to suppose it to be, all conditions 

 are satisfied. Moreover, it would seem that to suppose 

 the ether atoms never to interfere with each other's 

 motion of translation would be equivalent to assuming 

 that their mean path is indefinitely great, which appears 

 to involve the assumption that the atoms have no finite 

 size or dimensions, which would put a difficulty in the 

 way of a satisfactory or consistent conception of matter. 

 On this ground I would therefore suggest that the atoms- 

 of ether may be considered to have a reasonably long 

 free path [which may be conceived as great as we please^ 

 by simply conceiving the atoms small], and thus the dis- 

 sipation of the energy of the light may be reduced within 

 the limits required by observation. This does not alter 

 in the least in its essential details the above suggestion 

 by Prof. Maxwell as to the mode of production of the 

 transverse vibrations of light, which I would accordingly 

 enlarge upon and elaborate somewhat here (in connection 

 with the special structure of gross matter required by the 

 physical theory of gravity). First it is important to ob- 

 serve that many observed facts lead us to infer that gross 

 matter (probably the molecules - themselves) possesses 

 a more or less open structure (or possesses a high degree 

 of porosity). The transparency of some bodies, the free 

 passage of the magnetic disturbance through all bodies, 



■ I merely substitute " atoms cf ether" in the above passage for " mole- 

 cule-." to avoid any possible ambiguity, as the word "molecules is itten 

 applied to the parts of gross matter. 



- this is also in harmony with the modern theory of vortex-atoms. 



