Bauhaus-Universität Weimar

Psychological Equipment: Catalog No. 48, Marietta Company, Marietta, Ohio
Marietta Apparatus Company, Marietta, Ohio 
8- 7 PHOTOCHROMATIC INTERVAL APPARATUS. This consists of a small lamp house, 
with iris diaphragm, and rotatable disk carrying gelatine covered apertures through which the 
light from a small electric lamp shines. Between the light and the iris diaphragm opening is a 
movable neutral tint glass wedge giving light transmissions from total down to one one-thousandth. 
The light is accordingly measurable in either intensity or area. The colored gelatine filters have 
definite wave length transmission values, red 700-600 mm., yellow 700-500 mm., green 600-500 
mm., blue 500-400 mm. 
9- 3 BENHAM DISK. The “flight of colors” or “color decay” characteristic of strong positive 
after-images of white is exemplified in this disk in which the different durations of after-images 
resulting from different lengths of circular lines are shown to produce variations in hue. The 
components of white “decay” at different rates. 
9-4 BEZOLD FIGURE CARD. This figure is about 5 inches in diameter and when placed at 
about 20 feet distance and viewed monocularly, fixation on the center, there appears a variety 
of faint colors on the edges of the white rings. (See Titchner, Experimental Psychology.) 
9-5 SIMULTANEOUS INDUCTION DISKS. This equipment is suitable for class room demon¬ 
stration. It consists of simple rotator with set of standard color disks. A large and small disk 
(uncut) of each color is provided, with which a black, white pair (cut) of intermediate diameter 
is used. The gray zone thus produced may be rendered more or less equal in brightness to the 
color surface, illustrating the increased intensity of the induction effect on the gray zone under 
approximate equality of brightness. 
Cardboard $3.25; Celluloid $4.25 
9- 6 SIMULTANEOUS INDUCTION CARDS. A very simple device for illustrating this effect. 
The white surface below the card should be illuminated by a variable source (i. e. moving nearer 
to or farther from a light) and the surface of the card is kept at constant brightness (or the card 
surface may be varied and background white kept constant). By this simple means the star¬ 
shaped neutral area viewed through the aperture may be made equal to the colored surface in 
brightness, under which condition the induced hue on white (gray) star surface is at maximum. 
Standard red, yellow, green, and blue cards are provided in a set. Package contains three each of 
four colors in celluloid. 
10- 3 STEREOPSIS TEST CARD. This is one of the Keystone stereoscopic cards. (Half of the 
card shown in our illustration.) It provides an exceedingly accurate and measurable test of stere- 
10-4 FREEMAN EYE MOVEMENT MIRROR. As represented in the illustration this is a 
simple means of observing eye movement in reading. It consists of a head-band having bracket 
support for mirror in which subject’s eye movements can be seen by an observer from behind. 
(See Freeman’s “Experimental Education.”) 
CARDBOARD COLOR DISKS. Set of 14 disks, consisting of one large and one small each of the 
following colors: red, yellow, green, blue, purple, black and white. With cardboard measuring 
Price $3.25 
CELLULOID COLOR DISKS. Similar to above cardboard disks, with purple omitted. 
Price $4.25 
NEGATIVE AFTER-IMAGE CARDS. Set of twelve cards, 3 each of 4 colors. 
Price $4.00 


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