214 
Schneider, Ph.D. (Columbia), has been called to 
the chair in Northwestern University vacant 
through the resignation of Professor Kraemer. 
Dr. L. SCHLESINGER, of Bonn, has been 
appointed full professor of mathematics at 
Klausenburg ; Dr. Detmer, associate professor 
of botany in the University of Jena, has been 
promoted to a full professorship; Dr. Lassar 
Cohn, professor of chemistry in the University 
at Konigsberg, has been elected director of the 
Liebig Akademie of Munich; Dr. A. O. Kihl- 
man has been appointed associate professor of 
botany at Helsingfors, and Dr. G. J. Ptaschicky, 
professor of zoology in St. Petersburg; Dr. 
F. y. Luschan, docent in the University of 
Berlin, has been promoted to a professorship of 
anthropology ; Dr. Seelhorst, director of the 
Agricultural Experiment Station at Gottingen 
has accepted a professorship in the Agricultural 
College at Hohenheim. 
DISCUSSION AND CORRESPONDENCE. 
COLOR STANDARDS. 
Iris a matter for congratulation that the 
subject of color standards and definitions has 
been brought before the public for discussion in 
SCIENCE* Education in any branch of knowl- 
edge becomes simple and successful in propor- 
tion as its terminology is definite and intelligible. 
It would be quite interesting to set forth the 
plans that have been offered for obtaining color 
standards ; one proposes to take an orange as 
the type of that color, and in like manner to let a 
lemon, an olive, etc., be the ultimate definition 
of those hues. One has even suggested a col- 
lection of wines of various colors as standards, 
and the matching of other colors by mixing the 
wines, an operation as dangerous as it is un- 
scientific. 
In the search for standards we must first be 
able to define completely a colored surface ; not 
by saying that it resembles or differs to a certain 
extent from some other arbitrary surface, but it 
must be defined in terms of certain invariable 
and readily reproducible standards. 
To describe completely a surface we must 
give value to four factors which go to affect the 
impression which it produces upon the normal 
* See article in Screncnr, July 16, p. 89, 
SCIENCE. 
(N.S. Voz. VI. No. 136. 
observer: First, the predominating wave-length 
or wave-lengths of the light coming from it ; 
second, its total luminosity, as compared with 
some standard; third, its saturation, or the 
ratio of the colored light to the total luminosity ;. 
fourth, its texture. 
The matter of texture may be eliminated by 
placing the surface far enough from the eye, or, 
better, by rotating it so rapidly that the eye 
cannot distinguish the texture; consequently a. 
standard of texture is unnecessary. A standard 
of total luminosity is easily obtained by holding 
a cold surface over burning magnesium or zine ; 
the coating of oxide thus produced has been 
adopted as ‘ white’ by Rood, Mayer and others. 
In other words, the luminosity of such a surface 
is taken as 100 %. A box about five feet in 
length and one in cross-section, lined with black 
velvet and provided with an opening about four 
inches in diameter in one end, when so mounted 
that light cannot shine directly into the open- 
ing, will furnish an admirable standard black, 
or 0% luminosity. Between these two ex- 
tremes fall all surfaces not incandescent. 
White cardboard and lamp-black form very 
convenient ‘ practical units,’ and their relation 
to the standards can at any time be easily and 
accurately determined. The question of satu- 
ration, or the ratio of the energy of the predomi- 
nating characteristic wave-lengths to the total 
visible energy, is serious. In fact, for the pres- 
ent we must be satisfied to agree upon some 
temporary standards which may ultimately be 
absolutely determined. 
As to the predominating or characteristic 
wave-length or wave-lengths we might, of 
course, refer everything to the spectrum and de- 
fine by it directly, but it would be a very 
elaborate and inconvenient method. It is, how- 
ever, customary to adopt a few typical wave- 
lengths and define by combinations of these. 
Theoretically three such colors are sufficient, 
but practical convenience makes it desirable to 
have five or six, Then a mixture of these, with 
the addition of black and white when necessary, 
enable the observer to match any color, shade, 
tint or hue. 
What shall govern the choice of the five or 
six working standards?. Of course, we expect 
red, green and blue; probably yellow, and pos- 
