Perc 

 Perf 



erception 

 Action 



SCIENTIFIC SIDE-LIGHTS 



516 



paint one part of it dark brown, another 

 part bright yellow, to give its real sensa- 

 tional effect. We take no heed, as a rule, 

 of the different way in which the same 

 things look and sound and smell at different 

 distances and under different circumstances. 

 The sameness of the things is what we are 

 concerned to ascertain, and any sensations 

 that assure us of that will probably be con- 

 sidered, in a rough way, to be the same with 

 each other. JAMES Psychology, vol. i, ch. 

 9, p. 231. (H. H. & Co., 1899.) 



2540. PERCEPTION OF COLORS LIM- 

 ITED Chemical or Ultraviolet Waves Invis- 

 ible. The first question that we have to 

 consider to-night is this: Is the eye, as an 

 organ of vision, commensurate with the 

 whole range of solar radiation is it capa- 

 ble of receiving visual impressions from all 

 the rays emitted by the sun? The answer 

 is negative. If we allowed ourselves to 

 accept for a moment that notion of gradual 

 growth, amelioration, and ascension implied 

 by the term " evolution," we might fairly 

 conclude that there are stores of visual im- 

 pressions awaiting man, far greater than 

 those now in his possession. Hitter dis- 

 covered in 1801 that beyond the extreme 

 violet of the spectrum there is a vast efflux 

 of rays which are totally useless as regards 

 our present powers of vision. These ultra- 

 violet waves, however, tho incompetent to 

 awaken the optic nerve, can shake asunder 

 the molecules of certain compound sub- 

 stances on which they impinge, thus pro- 

 ducing chemical decomposition. TYNDALL 

 Lectures on Light, lect. 5, p. 162. (A., 

 1898.) 



2541. PERCEPTION OF LIGHT IN 

 PAINTING ILLUSIVE Relative Judgment of 

 Light and Shade Determines Mental Effect. 

 It is found that the degree of luminosity 

 or brightness of a pictorial representation 

 differs in general enormously from that of 

 the actual objects. Thus, according to the 

 calculations of Helmholtz, a picture repre- 

 senting a Bedouin's white raiment in blind- 

 ing sunshine will, when seen in a fairly lit 

 gallery, have a degree of luminosity reach- 

 ing only to about one-thirtieth of that of 

 the actual object. On the other hand, a 

 painting representing marble ruins illumi- 

 nated by moonlight will, under the same 

 conditions of illumination, have a luminos- 

 ity amounting to as much as from ten to 

 twenty thousand times that of the object. 

 Yet the spectator does not notice these stu- 

 pendous discrepancies. The representation, 

 in spite of its vast difference, at once car- 

 ries the mind on to the actuality, and the 

 spectator may even appear to himself, in 

 moments of complete absorption, to be look- 

 ing at the actual scene. SULLY Illusions, 

 ch. 5, p. 88. (A., 1897.) 



2542. PERCEPTION OF TIME AND 

 SPACE DISTURBED BY HASHISH Minutes 

 Seem Hours Distance Seems Interminable. 

 The disturbance of the perceptive facul- 



ties [by hashish] is remarkably shown in 

 regard to time and space. Minutes seem 

 hours, and hours are prolonged into years; 

 and at last all idea of time seems obliter- 

 ated, and the past and present are con- 

 founded together. M. Moreau mentions as 

 an illustration that on one evening he was 

 traversing the passage of the opera when 

 under the influence of a moderate dose of 

 hashish: he had made but a few steps, 

 when it seemed to him as if he had been 

 there two or three hours; and, as he 

 advanced, the passage appeared to him in- 

 terminable, its extremity receding as he 

 pressed forwards. But he gives another 

 more remarkable instance. In walking 

 along the boulevards, he has frequently 

 seen persons and things at a certain dis- 

 tance presenting the same aspect as if he 

 had viewed them through the large end of 

 an opera-glass ; that is, diminished in ap- 

 parent size, and therefore suggesting the 

 idea of increased distance. This erroneous 

 perception of space is one of the effects of 

 the Amanita muscaria, an intoxicating 

 fungus used by the Tatars; a person under 

 its influence being said to take a jump or a 

 stride sufficient to clear the trunk of a tree, 

 when he wishes only to step over a straw or 

 a small stick. Such erroneous perceptions are 

 common enough among lunatics, and become 

 the foundations of fixed illusions; whilst 

 in the person intoxicated by hashish there 

 is still a certain consciousness of their decep- 

 tive character. CARPENTER Mental Physiol- 

 ogy, bk. ii, ch. 17, p. 642. (A., 1900.) 



2543. PERCEPTION, POWER OF, 

 AMONG SAVAGES Arab Knows Footprint 

 of His Own Camels. In reading almost any 

 account of savages it is impossible not to 

 admire the skill with which they use their 

 weapons and implements, their ingenuity in 

 hunting and fishing, and their close and ac- 

 curate powers of observation. Some savages 

 even recognize individuals by their footsteps. 

 Thus Mr. Laing mentions that one day while 

 traveling near Moreton Bay, in Australia, 

 he pointed to a footstep and asked whose 

 it was. The guide "glanced at it without 

 stopping his horse and at once answered, 

 ' White fellow call him Tiger.' " This turned 

 out to be correct, which was the more re- 

 markable as the two men belonged to differ- 

 ent tribes, and had not met for two years. 

 Among the Arabs, Burckhardt asserts that 

 some men know every individual in the tribe 

 by his footstep. " Besides this, every Arab 

 knows the printed footsteps of his own cam- 

 els and of those belonging to his immediate 

 neighbors. He knows by the depth or slight- 

 ness of the impression whether a camel was 

 pasturing and therefore not carrying any 

 load, or mounted by one person only, or 

 heavily loaded." AVEBURY Prehistoric 

 Times, ch. 15, p. 519. (A., 1900.) 



2544 . PERCEPTION RELATIVE 



Light and Dark Determined by Contrast. 

 What appeals to our attention far more 



