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differ also in the dominant hues of the three components which they employ. In order to convert the data obtained by the application of any such system to terms of our three elementaries, it is necessary to employ nine coefficients which represent the degree of participation of each of our elementaries in each of the components of the given system or vice versa. The reverse conversion involves nine reciprocal coefficients based upon the same relationship. The operations involved may be represented by the following equations:—

(1) R=ar+bg+cv

(2) G=dr+eg+fv

(3) V=hr+ig+jv

where a, b, c, etc., are the coefficients in question, r, g, and v are the values of the given trichromatic measuring system, and R, G, and V are the desired excitation values.

Table 15

Coefficients for Interconverting Ives Colorimeter Data and Excitation Values

If r, g, and b are the components of a color according to the Ives colorimeter, and R, G, and V are its values in terms of the elementary excitations used in this Report;

R=	1870r	+	2080g	+	14b
G=	134r	+	3710g	+	124b
V=			506g	+	3460b

Conversely:

r	=	1275R	-	719G	+	21V
g	=	-46R	+	646G	-	23V
b	=	7R	-	95G	+	665V

There is an arbitrary factor in all of the above coefficients, so that the results are significant only as proportionalities.

The only trichromatic additive system which is in any way well known at the present time is that employed in the Ives colorimeter. Table 15 provides values for the coefficients which must be employed to convert color specifications in terms of the Ives system into excitation terms by use of the formulae given above. These coefficients were obtained by applying the excitation data of Table 6 to the spectrophotometric curves for the filters and light source employed in the Ives colorimeter in accordance with the principles outlined under Section A of the present part of this report. The light source assumed was average noon sunlight.