174 COLOR PHOTOGRAPHY. 



He calls the process here designated as mechanical adaptation, so 

 far as it plays a part with living- beings, "intra selection," 1 and refers 

 to a work of Wilhelm Eoux, which appeared in 1881, "Der Kampf der 

 Theile im Organismus, ein Beitrag zur Vervollstandigung der mecha- 

 nischen Zweckmiissigkeitslehre." 2 The latter designates the process as 

 "functional adaptation," and discusses it in a general way as caused 

 by the " strife of the molecules," " strife of the cells." 3 As "molecules" 

 he understands the smallest organic process units. In the case at 

 hand, "molecules" is to be taken literally. 



Indeed, the result of colored illumination in a body may be figura- 

 tively expressed as the victory of the similarly colored molecules over 

 those dissimilarly colored, won by reason of their capacity of best 

 reflecting the incident light. Thus the application of the explanation 

 of the older processes of color photography to the explanation of certain 

 adaptation-colors in nature leads to the arrangement of these phenom- 

 ena under general groups, which may be recognized as processes of 

 mechanical adaptation. 



I proceed now to the experimental verification and the exact founda- 

 tion and working out of the matters above mentioned. First of all, I 

 must express my thanks to Professors Arzruni, Grotrian, Holzapfel, 

 and Wiillner, of the technical college of Aachen, for their assistance. 

 Since, unfortunately, I found it hard to judge of many of the finer 

 differences of color, I have given no observations of color unless they 

 had been made or checked by one or more of these gentlemen. 



II. — Apparatus and Procedures. 



For the photography of the spectrum a Steinheil spectrum apparatus 

 was used, iu which the ocular was replaced by a small photographic 

 camera. This could be screwed to a tube which fitted in the telescoj>e 

 tube. The adjustment was performed by means of a rack and pinion 

 motion. 



The width of the slit was about 1 millimeter when great brightness 

 was wished and about 0.5 millimeter when a spectrum of greater purity 

 was desirable. The length of the spectrum from A to H 3 was 19.2 

 millimeters. Its height was generally between 15 and 18 millimeters. 



The source of light was usually the electric arc of a large Schuckert 

 lamp, used with an average current strength of 30 amperes, and whose 

 positive carbon had a thickness of about 23 millimeters. The carbons 

 had an inclination of 45° to the vertical, so that the greatest light 

 intensity was sent out in a nearly horizontal direction. The time of 

 exposure varied from a half hour to an hour in general, though under 

 the most favorable conditions colors were produced after a few minutes. 



1 Loc. cit., page 6. 



2 W. Roux, Leipzig. Published by Wilhelm Engelmanu. 



3 The strife of the tissues and the strife of the organs is, as Roux remarks, not to 

 be included in the same category, because dissimilar *parts then enter into combat. 



