Prof"pr Kepers luis solved tae probloin fit seciüg throtigh i mill-stone. In a paper read before tha Boieotifio Ascopiatiftn t Newport hu says: - 'Tiikc ii sheet of fookcap or letter paper; roll it up so tbitt tha opening it one oud shall bu 'arge enouifli to tako n the inllsizo of tliu eye, and at the nther end let the oponirg bo not half goluie. Talco it in ttm right baod, holding t bttween tha ttnunb md forefinajer place tli largo oud to the right eve, :imi lonk throujih it b"th eyefl open toward tho light Y"U ïcdl see a küle tiTovgh yonr hand. 'ifyou take it in left hand, and hold it to your left eye, it will bo the saino. Yon will in botb cases hd astonished to ue tht y o j haven hole in your hand. The ülusion is most complete." Froni thiii and other experiments, he conclndes that fin mpression made on tho retina of eitliereye cannot of itself enablo tis to determine on which retina it is roceived, and that the vigual peroeption lielongs to tho part of the optical npparatiiH near or within the bruin which belongs ia cominon to both oyes.