124 Observations and Experiments on Light. 



brightness considerably dimmed, and formed the intersecting 

 point of two rows of colored spectra, that crossed each other 

 nearly at right angles. One of the rows of spectra formed a very 

 acute angle with the shaft of the feather at its outer extremity, 

 and the other was nearly at right angles with the shaft. In each 

 colored spectrum the side nearest to the sun was a mixture of vio- 

 let and the contiguous rays of the prismatic spectrum, while the 

 side farthest from the sun was uniformly red. The sun was 

 slightly clouded when I made my first observations. Afterwards, 

 when the sun shone perfectly clear, I observed that the angular 

 spaces formed by the intersection of the two rows of colored 

 spectra were occupied by less brilliant spectra, arranged in the 

 same order as the two rows above described. 



On Monday, the Jst of July, 1839, I varied the experiments 

 above described, by making ray observations upon the flame of a 

 lamp, instead of the sun. I found an advantage in this, as it en- 

 abled me to change the distance of the luminous object at plea- 

 sure. In looking through the vane of the wing-feather of the 

 wild pigeon at the flame of the lamp, I observed spectra, colored 

 and arranged similarly to those which I saw when looking at the 

 sun. I first looked at the lamp at the distance of eight or ten 

 feet, and saw the two rows of colored spectra above described 

 entirely distinct from each other, with some faint appearances of 

 spectra in the angular spaces near the lamp. As I approached 

 the lamp, (hold+ng the feather to my eye and looking at the 

 flame,) the colored spectra in the two rows gradually approxima- 

 ted to the flame of the lamp and to each other, their colors at the 

 same time becoming less distinct and approaching to white light, 

 while the spectra in the angular spaces became more perceptible. 

 As I receded from the lamp, the spectra in the two rows receded 

 from the central flame and from each other, their colors at the 

 same time becoming more distinct, and the spectra in the angular 

 spaces gradually fading away. 



My next step was, in connection with my colleague, Prof. 

 Sturtevant, to introduce a small beam of light into a dark room 

 by passing it through the vane of the wing-feather of the Jay. 

 We observed colored spectra arranged upon a screen in the man- 

 ner described above. In the experiments which I first performed, 

 the eye was the dark chamber and the retina the screen. 



