536 



SCIENCE. 



[X. S. Vol. XVIII. No. 4fi0. 



A HITHERTO UNDESCKIBED VISUAL PHENOMENON. 



To THE Editor op Science: So far as I 

 know, the curious visual fact I am about to 

 describe has not been noted by psychologists, 

 and as it may, and seems to me really to be 

 of practical as well as psychologic importance, 

 I wish to ask your readers to verify and, pos- 

 sibly, to explain it. 



For several years I have observed the fol- 

 lowing peculiar appearance of a distant light ' 

 at night: The electric (incandescent) lamps 

 of a town two or three miles away and below 

 me, when observed fixedly and singly, have 

 distinct appearances of movement, if seen 

 under certain conditions. These conditions 

 are as follows: 



1. The observer must sit in the darkness, 

 i. e., without visible objects about, which would 

 fix a number of objects in the attention and 

 prevent the needed indefiniteness, or lack of 

 ' fixing ' necessity., 



2. The night must be dark, moonless, etc., 

 so that there is no multiplicity of distant 

 objects to arouse the definite ocular fixation, 

 or localizing necessity, which prevents the 

 indefiniteness, the lack of sensational or top- 

 ographic features required to produce the 

 phenomenon in question. 



3. By means of the hand, interposed shades, 

 etc., one must shut out of the ' field of vision,' 

 as well as possible, all other lights except the 

 one to be observed. 



4. The movements of the distant light are 

 made more manifest and pronounced by: (a) 

 closing one eye; (b) not winking; (c) im- 

 mobility of the head; (d) steadiness and con- 

 tinuousness of the gaze. 



The distant light must be strong and rich 

 enough so that (as happens with weak powers) 

 the image does not fade to invisibility with 

 constant fixation. A star as an object is not 

 so good as a brilliant electric light, because, 

 most stars are too weak in light-power, or 

 other stars are too near by to secure the single- 

 ness of object desirable, etc. I have become 

 able by practice to observe the movement in a 

 star, but a beginner will succeed better with 

 a distant electric light. To myself and some 

 friends the movements are observable with 



both eyes open, but they are more pronounced 

 with a single eye, and besides they have gen- 

 erally a peculiar character with a single eye. 

 Perhaps half the friends who have made the 

 tests do not observe the more decided move- 

 ments of myself and others. These speak 

 only of a quivering or of slight vibratory 

 movements. The appearances of movements 

 are not those of ' twinkling,' changes in the 

 rays, etc., and only a little experience is re- 

 quired to convince one that they are not 

 caused by clouds, atmospheric radiation or 

 other conditions — in a word they are not ' ob- 

 jective.' 



The character of the apparent movements, 

 as they appear to myself and other friends 

 who see them as plainly as myself, is as 

 follows: With the right eye (the head being 

 level, or erect), the light will somewhat slowly 

 move, with varying rapidity, and without 

 regular rhythm or ' beat,' to the right, and 

 often upward — the motion being like that of 

 a small balloon or floating downy seed, in a 

 breeze, moving according to the force, gusts 

 or eddies of the wind. With the left eye alone 

 the movements are usually but not always to 

 the left and also sometimes upward. I suspect 

 the character of the movement^ will depend 

 upon whether one is right-eyed or left-eyed. 

 (I am convinced that either by necessity or 

 habit one is always partly or preponderantly 

 right-eyed or left-eyed, just as one is right- 

 handed or left-handed — but this, ad, interim. 

 is ' another matter.') I have made a number 

 of experiments as to the influence of position 

 of the head upon the movements, but the con- 

 sideration of these may also be omitted. 



As to the explanation of the -phenomenon : 



1. It is not, I think, due to the spreading of 

 the tears over the cornea in an irregular man- 

 ner; nor to their drying, producing a slight 

 warping of the same or irregularity of trans- 

 parency. 



2. ISTor to lymph-movements in the sub- 

 stance of the cornea. 



3. Nor to muscffi volitantes — which are not 

 uniform in direction, etc. 



4. Nor to movements of the blood cor- 

 puscles in the capillaries of the retina, for 



