36 F. E. Nipher — Phenomena of Binocular Vision. 



with one eye, and toward the open hand with the other eye, 

 the edge of the hand being in contact with the tube. The 

 dissimilar objects producing unlike images upon the retinae, the 

 sensations blend and a hole will appear to be cut through the 

 palm of the hand, through which the tube passes. That part 

 of the tube between the eye and hand will appear to be trans- 

 parent, as though the hand were seen through it. 



This experiment is very old, but seems not to have found its 

 way into scientific literature. 



2. Keplace the hand by a sheet of unruled paper, upon which 

 a drop of ink has been placed. By proper management, the 

 ink blot may be made to appear within the tube, by so plac- 

 ing the paper that the hole which is apparently cut through it, 

 coincides with the blot. Ordinarily the blot will then appear 

 opaque, the paper immediately around it, and apparently within 

 the tube, being invisible. The blot appears as it were suspended 

 in space. By concentrating the attention strongly on object! 

 seen through the tube, especially if they are strongly illumin- 

 ated, the blot becomes more hazy, transparent, and may even 

 be made to disappear altogether. "The mental effort necessary 

 to do this cannot be maintained more than a few seconds, and 

 the spot will reappear. If the effort to cause the spot to thus 

 disappear be kept up, the attention being strained to its highest 

 pitch, the blot will disappear and reappear at regular intervals 

 of a few seconds, the absolute time depending upon the illumina- 

 tion. It seems as though the organs exerted become fatigued, 

 and relaxing for a few moments, refreshment sets in, which 

 again renders possible the exertion necessary in causing the 

 blot to disappear. It is possible that these experiments maybe 



so ' "' ;is '" throw some light upon the conditions necessary 



in fixing the attention. Interesting experiments may also be 

 made by substituting a fragment of a plane mirror for the sheet 

 of paper. Looking through a rather large tube at a distant 

 object with the right eye, and the reflected image of the left 

 eye will appear staring up the tube, the adjoining parts of the 

 head being invisible. 



3. Substituting lor the ink-blot a small hole cut through the 

 paper, the small hole can also be made to appear within the 



- 

 rounding paper being invisible, unless attention be directed too 

 to the paper in which the hole is cut. The relative 

 >n of the small hole, and the space in 

 around it depends upon the relative illumination of objects upon 

 which the tube is directed, and that of the sheet of paper 

 exposed to the other eye. 



4. Keeping the same arrangement, place at a distance of one 

 foot from the end of the tube a sheet of paper so that objects 



