321 



SCIENTIFIC SIDE-LIGHTS 



Illusion 

 Imagination 



plained as the shadow of a tree in the sum- 

 mer sunshine, it has an uncanny appear- 

 ance. It is called the " Specter of the 

 Brocken," and has been looked upon with 

 superstitious awe by the ignorant people for 

 ages past. This specter may be seen both 

 at sunrise and at sunset, but of course on 

 opposite sides of the mountain. ELISHA 

 GRAY Nature's Miracles, vol. ii, ch. 27, p. 

 215. (F. H. &H., 1900.) 



1565. ILLUSIONS OF SIGHT Spec- 

 trum Seen in Darkness Newton's Experi- 

 ence. Sir Isaac Newton was able to recall 

 [the spectrum] by going into the dark and 

 directing his mind intensely, " as when a 

 man looks earnestly to see a thing which is 

 difficult to be seen," and this [image], after 

 a frequent repetition of this process, came 

 ( he says ) to return " as often as I began to 

 meditate on the phenomena, even tho I lay 

 in bed at midnight with my curtains 

 drawn." For altho phenomena of this class 

 are often regarded as ocular spectra pro- 

 duced by retinal change, their reproduction 

 by mental states seems to place them in the 

 same category as the visual sensations 

 which are distinctly reproduced by memory 

 that is, by cerebral change. In fact, there 

 is such a gradational transition from the 

 one state to another that it seems clear that 

 they have a common origin. CARPENTER 

 Mental Physiology, bk. i, ch. 4, p. 165. (A., 

 1900.) 



1566. ILLUSIONS OF TOUCH False 



Interpretation of True Perception. The dif- 

 ferent degrees of sensitiveness possessed by 

 different parts may give rise to errors of 

 judgment in estimating the distance between 

 two points where the skin is touched. Thus, 

 if blunted points of a pair of compasses 

 (maintained at a constant distance apart) 

 be slowly drawn over the skin of the cheek 

 toward the lips, it is almost impossible to 

 resist the conclusion that the distance be- 

 tween the points is gradually increasing. 

 When they reach the lips they seem to be 

 considerably further apart than on the 

 cheek. Thus, too, our estimate of the size 

 of a cavity in a tooth is usually exaggerated 

 when based upon sensation derived from the 

 tongue alone. Another curious illusion may 

 here be mentioned. If we close the eyes, and 

 place a small marble or pea between the 

 crossed fore and middle fingers, we seem to 

 be touching two marbles. This illusion is 

 due to an error of judgment. The marble is 

 touched by two surfaces which, under ordi- 

 nary circumstances, could only be touched 

 by two separate marbles, hence the mind, 

 taking no cognizance of the fact that the 

 fingers are crossed, forms the conclusion 

 that two sensations are due to two marbles. 

 BAKER Handbook of Physiology, vol. ii, 

 ch. 19, p. 165. (W. W., 1885.) 



1567. ILLUSIONS USED IN HEATHEN 

 RITES Images of Gods Formed by Concave 

 Mirrors. A stick half immersed in water 



always looks broken, however well we may 

 know that the appearance is due to the 

 bending of the rays of light. Similarly, an 

 echo always sounds as tho it came from 

 some object in the direction in which the 

 air-waves finally travel to the ear, tho we 

 are perfectly sure that these undulations 

 have taken a circuitous course. It is hardly 

 necessary to remind the reader that the 

 deeply organized tendency^ to mistake the 

 direction of the visible or audible object in 

 these cases has from remote ages been made 

 use of as a means of popular delusion. 

 Thus, we are told by Sir D. Brewster, in his 

 entertaining " Letters on Natural Magic " 

 (letter iv), that the concave mirror was 

 probably used as the instrument for bring- 

 ing the gods before the people. The throw- 

 ing of the images formed by such mirrors 

 upon smoke or against fire, so as to make 

 them more distinct, seems to have been a 

 favorite device in the ancient art of necro- 

 mancy. SULLY Illusions, ch. 5, p. 73. (A., 

 1897.) 



1568. IMAGES OF MEMORY MAY 

 HAVE A KIND OF OBJECTIVE PRESENT 

 EXISTENCE It is only when the sting of 

 the recollection is removed, when, for ex- 

 ample, the calling-up of the image of a lost 

 friend is no longer accompanied with the 

 bitterness of futile longing, that a healthy 

 mind ventures to nourish recollections of 

 such remote events and to view these as 

 part of its recent experiences. In this case 

 the mnemonic image becomes transformed 

 into a kind of present emotional possession, 

 an element of that idealized and sublimated 

 portion of our experience with which all 

 imaginative persons fill up the emptiness of 

 their actual lives, and to which the poet is 

 wont to give an objective embodiment in 

 his verse. SULLY Illusions, ch. 10, p. 261. 

 (A., 1897.) 



1569. IMAGINATION, CREATIVE Mo- 

 zart's Composing. Mozart describes thus 

 his manner of composing: First, bits and 

 crums of the piece come and gradually join 

 together in his mind; then, the soul getting 

 warmed to the work, the thing grows more 

 and more, " and I spread it out broader and 

 clearer, and at last it gets almost finished 

 in my head, even when it is a long piece, so 

 that I can see the whole of it at a single 

 glance in my mind, as if it were a beautiful 

 painting or a handsome human being; in 

 which way I do not hear it in my imagina- 

 tion at all as a succession the way it must 

 come later but all at once, as it were. It 

 is a rare feast! All the inventing and 

 making goes on in me as in a beautiful 

 strong dream. But the best of all is the 

 hearing of it all at once." JAMES Psychol- 

 ogy, vol. i, ch. 9, p. 255. (H. H. & Co., 

 1899.) 



15 7O. IMAGINATION DISTORTING 



FACT Seaman's Strange Tale Scientific Ba- 

 sis of Story. Another animal, a zoophyte, 

 consists of a thin, straight, fleshy stem, 



