Page:Encyclopædia Britannica, Ninth Edition, v. 22.djvu/564

 [...] A. Stroh (without knowing that H. Grubb had described the essentials of the apparatus in 1879) has recently invented a new form of sterescope based on the well-known effects

of the persistence of vision. Two stereoscopic pictures are simultaneously projected by two lanterns on a screen so as to overlap, and disks having suitable slits are rotated in front of the lanterns and also in front of the eyes of the observer, in such a way that only one picture is thrown on the screen at a time, and also that the view of the picture is seen with the right and left eyes alternately. Further, the connexion between the disks is so arranged that the time of obscuring the view of the observer's right eye or left eye coincides with tho time when the light is shut off from the right or left lantern, and thus the left eye sees the picture of the left lantern and the right eye that of the right lantern. The two eyes never see at the same time, and each eye views its picture after the other, but the impressions come so fast as to be fused in consciousness, and the result is, the image stands out "in solid relief" (Proc. Roy. Soc., No. 244, vol. xl., April 1, 1886). [...]