MAYER: COLOR AND COLOR-PATTERNS. 173 



(5) Spectrum Analysis of Colors of Lepidoptera. I have made 

 some spectrum analyses of the light reflected from the wings 

 of various butterflies, by means of a piece of apparatus most kindly 

 suggested for the purpose by Prof. Ogden N. Rood of Columbia 

 College. The arrangement is shown in Figs. 1, 2, Plate 1; Fig. 1 

 being a perspective view, and Fig. 2 a horizontal section of the 

 ajjparatus, which consists of a rectangular box, blackened upon the 

 inside, and having a well-fitting cover. A rectangular slit (O) was 

 cut through one of the long sides of the box, near one end, and the 

 other end of the same side was perforated in order to allow the 

 admission of the direct- vision spectroscope (S). Imagine that we 

 wish to examine the yellow spots from a butterfly's wing. All of 

 the yellow sj^ots from the wing are cut out, and pasted upon two 

 pieces of cardboard so as to make two large unbroken patches of 

 color. The pieces of cardboard are then blackened upon all those 

 places where the colored wing was not pasted. One of the card- 

 boards is then suitably mounted ujDon the back of the box at B ; the 

 other is placed upon a vertical support (F), the plane of which is 

 parallel to the back of the box. 



The working of the apparatus is as follows : the sunlight enters 

 by the slit (O) and is reflected and diffused three or four times 

 between the pieces of colored wing mounted upon the back (B) of 

 the box, and the vertical support (F). The manner of this reflec- 

 tion and diffusion is shown by the dotted lines of Fig. 2. After 

 undergoing several reflections, the light enters the direct-vision 

 spectroscope (S). The slit of the spectroscope is wide open, and 

 thus the light which enters it may readily be examined. It was 

 found that it was necessary that the light be reflected more than 

 once from the wing before it enters the spectroscope, for the first 

 reflection shows so much white light that it is usually quite impossi- 

 ble to analyze the true color of the wing, the predominant colors 

 being obscured by a continuous spectrum. In general it was found 

 that the colors of the wings are not simple, but compound ; that is 

 to say, they are made up of a mixture of several different colors. 



For example, the spectrum of the rufous ground color of the 

 upper surface of the wings of Danais plexippus consists of all of the 

 red and j-ellow of the spectrum and about 75% of the green. 



The red spots upon the upper side of the fore Avings of Heliconius 

 melpomene also consist of the red and yellow and a very faint, 

 hardly visible, trace of green. 



