296 JAfc and Letters of Francis Galton 



general impressions of the mind founded upon blended memories with blended 

 |)ortrait8. He writes : 



" In the pre-8cientific stage of everj' branch of knowle<lge, the |>revalent notions of plienomena 

 M« founiied u}>on general imprcsoions; but when that stage is passed and the phenomena art 

 meMured and numbered, many of those notions are found to be wrong, even absurdly so. This 

 ia the oue not only in professional matters, but in those with wliich everyone has some oppor- 

 tunity of becoming acc|uainted. Think of the nonsense spoken every day alwut the signs of 

 Cuming weather, in connection, for example, with the pha.se.s of the moon. Think of the ideas 

 about chance, held by those who are unae(|uainte<l with the theory of proljabilities ; think of 

 the notions on hertsfity l)efore the days of Darwin. It is unnecessary to multiply instances ; 

 the frequent incorrectne.ss of notions derived from general impressions may lie assumed, and 

 the obji<ct of the following discourse is to point out a principal cause of it. 



Attention will he called U^ a source of error that is inherent in our minds, that vitiates the 

 truth of all our general impres,sions, and which we can never wholly eliminate except by 

 separating the confused facts upon which our general impressions are founder! and treating; 

 them numerically by the regular methods of statistics. It is not sutticient to learn that an 

 opinion has been long established or held by many, but we must collect a large number of 

 instances to test that opinion, and numerically compare the successes and failures." (p. 101.) 



Galton assumes the |)hysioloi.jical ba.sis of memory to 1)6 of the following 

 character : 



"Whenever any group of brain-elements has lx*n excited by a sense-impression, it becomes, 

 •o to speak, tender, and liable to be easily thrown again into a similar state of excitement. If 

 the new cause of excitement differs fn)ni the original one, a memory is the result. Whenever 

 a single cause throws different groups of brain-elements simultaneousl}- into excitement, the 

 result must be a blended memorw We are familiar with the fact that faint memories are very 

 apt to become confused. Thus some picture of mountain and lake in a country which we have 

 never visited often recalls a vague sense of identity with much we have seen elsewhere. Our 

 recollections cannot Ix; di8entangl(>d, though general resembhmces are recognised. It is also a 

 fact that the memories of persons who have great powers of visualising, that is of seeing well- 

 defined images in the mind's eye, are no less cajwhle of being blended together. Artists are, as 

 a class, pos8esse<l of the visualising power in a high degrets and they are at the sjime tirno 

 pp&«niinently distinguished by their gifts of generali.sation. They are of all men the inosi 

 capable of pro<lucing forms that are not copies of any individual, but repre.sent tlie charact<'risii< 

 features of classes." (p. 162.) 



Galton holds that the brain has the capacity for blending memories 

 together, and that general impressions are faint and perhaps faulty editions 

 of blended memories. Thus there is some analogy between general im- 

 pressions and composite photographs, both are generic images. 



" A generic mental image may he considered to Ixi nothing more than a generic portrait 

 stamped on the brain by the successive impressions made by its component images'." 



But while the photogi-aphic generic image gives each component a weight 

 proportional to its exposure, (Jalton says that the mental composite does not 

 give weight in the same manner. 



"The physiological effect of prolonge<l action, or of reiteratiim, is by no means in direct 

 proportion to the length of the one or to the fre<)uency of the other." 



He then cites the Weber- Fechner Law of the geometrical mean' as one 

 at least of the sources of error in general mental impressions. 



"Exceptional occurrences leave an impression on the brain of far greater strength, and 

 habitual occurrences of far less strength, than their numliers warrant." 



' Oalt4>n here cites Huxley (Ilumf, p. 9.')) as independently reaching the same conclusion. 



* llluRtratwl in the lecture itself by spinning discs painted black and white in concentric 

 ringN, one gi wng an arithmetical the other a geometrical series of tints ; the eye repudiates the 

 furuior an a graduated scale. 



