22(3 NATURAL HISTORY OF 



A good deal of discussion has arisen as to the method by 

 which this sailing flight is maintained, and perhaps the 

 question can hardly be considered as fairly settled. Dr. 

 Pettigrew has observed, in his interesting and valuable 

 memoir. On the Mechanism of Flight, that in sailing or gliding 

 birds " the pinion acts as a long lever, and is wielded with 

 great precision and power, particularly at the shoulder." 



And further, that a careful examination of the movements 

 of skimming birds has led him to conclude — 



" That by a judicious twisting or screw-like action of the wings at the 

 shoulder, in which the pinions are alternately advanced towards and 

 withdrawn from the head in a manner analogous to what occurs at the 

 pelvis in skating without lifting the feet, birds of this order can not 

 only maintain the motion, which they secure by a few energetic flap- 

 pings, but, if necessary, actually increase it, and that without either 

 bending the wing, or beating the air." * 



Whether, however, this is a correct or sufficient explanation 

 of what appears at first sight a very perplexing phenomenon, 

 I do not venture to offer any opinion. 



During most of the 20th we were greatly off our course, 

 beating in towards the land. On the 21st we noticed a 

 stormy petrel {Thalassidroma Wilsonii?) for the first time, 

 and on the afternoon of the following day a number of petrels 

 of another species, brown above, and white beneath, with the 

 exception of the throat, which was dark-coloured, were ob- 

 served flying about astern. We remarked that they soared at 

 a much greater elevation than either the Cape pigeons or 

 Fulmars. We never noticed them light on the surface of the 

 water, and their wings appeared proportionally much longer 

 and narrower. Immediately after the sun went down there 

 was a magnificent flush on the sky, which, at first pale pink, 



* Linn. Trans, vol. xxvi. p. 258. 



