THROUGH THE YEAR 239 



crested grebes, watched at this season through 

 glasses, take on those very lovely, volatile colours 

 which, in the right state of light, we see on the 

 plumage of swans, coots, and pochards. That of the 

 swans is far the finest, the intense glows of pure 

 blue and yellow shot over the pure white being so 

 extensive. The colours about the grebes I have only 

 noticed quite lately, looking at them when the sun 

 has been behind shifting clouds. All round the head 

 and neck of the birds appears a rim of volatile or 

 spirituous yellow, of the deeper orange hue of canary 

 yellow, perhaps ; whilst about the back of the bird 

 is a film of intense violet. But, the grebe shifting 

 round, this violet will sometimes take the place of the 

 yellow about the head and neck, so that the hues 

 appear to shift more often than I have seen them 

 shift on the swans. 



Besides swans, pochards, coots, and grebes, black- 

 headed gulls show the same colours in like states of 

 light, when they are watched through glasses. I 

 am not sure, but I think that the volatile hue which 

 I noticed on the gulls as they flew along the edge of 

 the sea in December was the rosy one. Why are 

 volatile colours shown on these water birds ? I 

 have not seen them on land birds, though perhaps 

 they appear on some that are high polished, as rook, 

 dove and lapwing. Is the cause of this colour in 

 the oiliness which lies about the plumage of many 

 water birds ? Such oily films often show the 

 brilliant " interference colours." A little pool of 

 spilt petrol on the dusty highway shows them 



