^'°ls.f'^'] Fourfccith Congress of the A. O. U. 85 



Some bird-drawings, the work of Mr. Ernest E. Thompson, 

 were shown by Mr. Frank M. Chapman. 



A vote of thanks was given Mr. Dutcher for the admirable 

 manner in which his accounts with the Union had been kept 

 during his long service as Treasurer. 



The feature of the afternoon session was the open-air talk by 

 Mr, Abbott H. Thayer, demonstrating his theory of the principles 

 of protective coloration. Mr. Thayer placed three sweet potatoes, 

 or objects of corresponding shape and size, horizontally on a wire 

 a few inches above the ground. They were covered with some 

 sticky material, and dry earth from the road on which they stood 

 was sprinkled over them so that they would be the same color as 

 the background. The two end ones were then painted white on 

 the under side, and the white color was shaded up and gradually 

 mixed with the brown of the sides. When viewed from a little 

 distance these two end ones, which were white below, disappeared 

 from sight, while the middle one stood out in strong relief and 

 appeared much darker than it really was. Mr. Thayer explained 

 that terrestrial birds and mammals which are protectively colored 

 have the under parts white or very light in color, and that the 

 color of the under parts usually shades gradually into that of the 

 upper parts. This is essential in order to counteract the effect 

 of the shadow, which otherwise, as shown by the middle potato, 

 makes the object abnormally conspicuous and causes it to appear 

 much darker than it really is. In the case of Mr. Thayer's 

 experiment some of the witnesses could hardly believe that the 

 striking difference in the visibility of the three potatoes was 

 entirely due to the coloring of the under side, and Mr. Thayer 

 was asked to color tlie middle one like the two others in order 

 that the effect might be observed. Mr. Thayer complied with 

 the request, painting the under side of the middle potato white, 

 and shading the white up into the sides as in the case of the 

 others. The effect was almost magical. The middle potato at 

 once disappeared from view. A similar experiment was tried on 

 the lawn. Two potatoes were painted green to resemble the 

 green of the grass above which they were suspended. One was 

 painted white on the under side and at once became invisible 

 when viewed from a little distance, while the other showed plainly 

 and seemed very dark, the shadow, superadded to the green of 



