6 STATISTICAL METHODS. 



Characters occupying three dimensions of 

 space may be quantitatively expressed by volume. The 

 volume of water or sand displaced may be used to measure 

 volume in the case of solids. The volume of water or sand con- 

 tained will measure a cavity. Irregular form is best measured 

 by getting, either by means of photography or drawings, pro- 

 jections of the object on one or more of the three rectangular 

 fundamental planes of the organ, and then measuring these 

 plane figures as already described. Or two or more axes may 

 be measured and their ratio found. 



Characters having weight are easily measured ; the 

 only precautions being those observed by physicists and 

 chemists. 



Color Characters. Color may be qualitatively ex- 

 pressed by reference to named standard color samples. Sucl} 

 standard color samples are given in Ridgeway's book, 

 " Nomenclature of Color," and also in a set of samples manu- 

 factured by the Milton Bradley Co., Springfield, Mass., costing 

 6 cents. The best way of designating a color character is by 

 means of the color wheel, a cheap form of which (costing 6 

 cents) is made by the Milton Bradley Co. The colors of this 

 "top" are standard and are of known wave-length as follows: 

 Red, 656 to 661 Green, 514 to 519 



Orange, 606 to 611 Blue, 467 to 472 



Yellow, 577 to 582 Violet, 419 to 424. 



It is desirable to use Milton Bradley's color top as a standard. 

 Any color character can be matched by using the elementary 

 colors and white and black in certain proportions. The pro- 

 portions are given in percents. In practice the fewest possible 

 colors necessary to give the color character should be employed 

 and two or three independent determinations of each should 

 be made at different times and the results averaged. So far 

 as my experience goes any color character is given by only 

 one least combination of elementary colors. (See Science, 

 July 16, 1897.) 



When there is a complex color pattern the color of the 

 different patches must be determined separately. In case of 

 a close intermingling of colors, the colored area may be rapidly 

 rotated on a turntable so that the colors blend and the result- 



