On the Phantascope. 157 
Exp. 
lines about two inches in length and three inches apar 
converging them in an attempt at superposition, I found the con- 
verged lines were not parallel but came in contact at the upper 
end first, and diverged a ‘little downward. Standing with my 
head erect, I repeated this experiment by converging voluntarily 
7—I placed a card having two perpendicular parallel 
head back ward and looking horizontally over my cheeks, the con- 
verged perpendiculars coincided throughout. I learned by this 
that both of my eyes do not rotate in one and the same horizon- 
tal plane. I got another person to repeat the same experiment, 
and he found the error of his eyes to be in the opposite direction, 
the converged perpendiculars meeting first at the bottoms. This 
hy a moral adage to be physically true, “we don’t all see 
1kKe,”’ 
This instrument and the researches into binocular vision, serve 
to extend considerably our knowledge of the anatomy and physi- 
ology of vision, nor is the subject by any means exhausted. I 
have not time to investigate the matter fully, and shall be happy 
to see fair and honorable competitors enter the field. e verifi- 
cations and variations of the experiments by your correspondent, 
Dr. Lathrop, were gratifying to me. 
This apparatus will illustrate many important points in optics, 
and especially the physiological point of “single vision by two 
eyes.” It shows also that we do not see an object in itself, but 
the mind contemplates an image on the retina, and always asso- 
ciates an object of such a figure, attitude, distance, and color as 
will produce that image by rectilinear pencils of light. If this 
image on the retina can be produced without the object, as in the 
Phantascope, then there is a perfect optical illusion, and an object 
18 Seen where it is not. Nay, more, the mind does not contem- 
plate a mere luminous image, but that image produces an un- 
known physiological impression on the brain. It follows that if 
the nerves can, by disease or by the force of imagination, take on 
this action, a palpable impression is made without either object 
or picture. As this would be most likely to occur when actual 
objects are excluded, as in the night, we have an explanation of 
the scenery of dreams, and the occasional “ apparitions” to waking 
persons. ‘The murderer, too, has a picture stamped on the sen- 
-Sorium by the sight of his victim, which ever wakes into vibra- 
tion when actual pictures are excluded by darkness. 
