1778 processes on barbs, barbules and so forth. These surfaces by re- fection and diffraction cause interference between the incident rays of white light and the rays reflected to the eye. That is the waves in the two sets of rays are out of phase and wherever a crest meets a trough (or a condensation meets a rarefaction) they destroy each other, just as water waves do, wholly or in part. As a result where we see pure spectrum red, for example, that is the re- sult of structural effects --in contradistinction to pigment effects- it means that all of the other colors which made up the white in- cident beam (neglecting absorption) have been destroyed and red alone has escaped to the eye. I am purposely neglecting absorption, internal reflection, which of course have effect, and consider only the primary cause of the metallic colors: interference. Absorption, internal reflection and the pigments in the feathers themselves, it seems to me, can have had in this instance, only slight effect; because if they had had the bird would have been black all over (as he was indeed at first). As the bird dried and the film of moisture on its feathers became thinner, the structural features of the feathers which caused interference had superimposed upon them a film which possessed its own diffraction properties (like the soap bubble film). This film for a period of about 15 minutes, as stated, was, in places varying in exact location with time, of such a thickness as to cause inter- ference of the (normally outstanding) red waves, thus destroying them and, either: (1) Leaving the blue waves (which are normally seen mix- ed with the red, giving the cerise, magenta, rosy crimson--whatever you choose to call it) outstanding and unaffected, or: (2) else added its own blue created for this one short period, or (3) or both. (All of this, of course, is speculation and only skims the surface of the vast complex of color). A suggested experiment. It will be observed that the color change was from one end of the visible spectrum to the opposite. It would be interesting to test out the foregoing crude, tentative theory by wetting the diffraction grating in a spectroscope and observing results. Now I wonder what new species would have resulted if I had shown this bird to a competent "classificationist" without telling him that it was wet! Rhody was not seen up here today, but kept himself subject to call on the west lot and was given a huge mouse. December 22nd to 29th, incl. This was a period of fair, sunny weather excepting for one forenoon. Temperatures running from minima of 45-50 to maxima of 56-68. Rhody continued to sleep in his No.1 house at night and show- ed a tendency to come up here earlier in the day. As a rule he was satisfied with one mouse but, on two days, preferred to go to the cage for meat. I have been watching him rather closely for signs of "Spring" awakening of reproductive instinct, such as: beginning of song, clapping of wings together over his back, hrooing when given a mouse followed or not by ritual, attention to the mirror, increased inter- rest in the magpies, and so forth; but as yet none of these symptoms has been observed with certainty.