Bauhaus-Universität Weimar

Dictionary of philosophy and psychology including many of the principal conceptions of ethics, logics, aesthetics ... and giving a terminology in English, French, German and Italian, vol. 1 [a-laws]
Baldwin, James Mark
haptical pieces (the word Haptics, q. v., being 
taken in its widest sense), and apparatus for 
the investigation of taste and smell, (e.b.t.) 
(a) Optical. The instruments employed in 
the study of psychological optics fall into the 
following groups :—■ 
(1) Apparatus for indirect vision. Near 
the periphery of the retina the power of 
space discrimination falls off considerably, and 
the colour-sense is entirely lost. These pheno¬ 
mena are investigated by means of the peri¬ 
meter ; this consists, essentially, of a fixation 
point for the eye, and a circular arm with scale 
rotating about the line of direct vision. To 
determine the peripheral limits of any colour, 
a small piece of coloured paper is placed at 
the end of the scale and gradually approached 
to the centre of vision until the colour is 
correctly distinguished; this is repeated for 
as many points of the periphery as desired. 
To determine the peripheral variations of the 
space threshold the coloured piece is replaced 
by a white surface having two black dots 
a small distance apart ; the piece is moved in 
till the spots are distinguished as two. The 
campimeter is similar to the perimeter ; 
instead of a circular scale, a large flat sheet 
of white paper is used; the colour limits, &c., 
are marked directly on this. Both perimeter 
and campimeter are used for mapping the 
Blind Spot (q. v.). A small dot on a white 
background is moved about near the centre of 
vision ; the points where it disappears and 
reappears indicate the edges of the blind spot. 
In this case the eye moves and the stimulus 
is constant. 
A useful instrument for general purposes 
is Hess’ indirect vision colour-mixer ( Arch. f 
Ophthal., xxxv). (h.c.w.) 
(2) Apparatus for the testing of Colour¬ 
blindness (q. v.). See also that subject 
under Vision. 
(3) Quality and wave-length; sense dis¬ 
crimination of spectral qualities ; instruments 
for analysing rays of light—the spectroscope, 
spectrometric apparatus, and—for combining 
them—the chromatoscope. Cf. Uhthoff, Arch.f. 
Ophthal., xxxiv ; Brodhun, Zeitsch.f. Psychol., 
iii ; Mentz, Philos. Stud., xiii. See Spectrum, 
and Light under Vision. 
(4) Purkinje phenomenon ; liminal values. 
As (3). Also dark room or dark box, with 
arrangement for graduation of light intensity 
(e. g. an episkotister, or partial disk com¬ 
posed of a retaining rim and variable black 
sectors) ; colour-mixers (rotating disks), 
Aubert’s diaphragm, and gelatine sheets. 
Bruecke, Sitzber. d. Wien. Akad. (1878), 3. 
Abth. ; Hillebrand, ibid., 3. Abth. (1889); 
Hering, Pflügers Arch., xlix and lx; König, 
Helmholtz-Festschrift (1891); König and 
Brodhun, Sitzber. d. Berl. Akad. (1888 and 
1889); Langley, Philos. Mag. (1889). 
(5) Apparatus for Colouk Mixture (q. v.). 
(6) Apparatus for contrast. Demonstra¬ 
tion pieces may be prepared from coloured 
cards. The phenomena can be well shown on 
rotating disks, or by means of shadows. An 
elaborate arrangement for quantitative work 
is described by Hess and Pretori, Arch. f. 
Ophthal., xl. See Lehmann, Philos. Stud., iii; 
Ebbinghaus, Sitzber. d. Berl. Akad., xlix ; 
Kirschmann, Philos. Stud., vi; Pretori and 
Sachs, Pflüger s Arch., lx. Cf. Meyer’s Experi¬ 
ment, Side-window Experiment. (e.b.t.) 
[(2) to (6)]. The threshold of difference of 
light intensity is found by comparing different 
shades of grey on the colour-wheel. This ajipa- 
ratus has an axle, on which black, white, and 
coloured disks or sectors may be clamped and 
rotated rapidly by means of a series of geared 
wheels or a motor. The disks used are slit 
along one radius, so that they can be fitted into 
one another, giving sectors of different colours 
or shades. The adjustable colour-wheel has 
an axle in three parts, one within another; 
the disks are fitted to each, interlocking as 
in the simple col our-wheel ; but by moving 
a lever the proportion of each disk visible 
may be altered while they are rotating. To 
find the threshold of difference, one black and 
one white disk are fitted together in a certain 
ratio, which is slowly altered till a difference 
is noted. The shade of grey is measured in 
terms of the proportion of black and white 
in the circumference. Another method used 
in this problem is to compare the shadows 
from two lights, one of which is varied in 
intensity or distance. 
The thresholds of colour-sensation and 
colour-difference, and various phenomena of 
saturation, colour mixing, contrast, &c., are 
investigated by means of colour-mixers. 
There are several forms, including the colour- 
wheel just described. The reflection colour- 
mixer, in its simplest form, consists of a 
clear pane of glass, standing perpendicular 
to a black velvet surface. Strips of differ¬ 
ently coloured paper are placed on the 
velvet at each side ; the subject looks 
through the glass at an angle and sees the 
reflection of one strip over the image of the 
other. The intensity of the reflected colour, 
and hence the character of the mixture, alters


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