° 1916 ] Huxley, Bird-watchitig atid Biological Science. 143 



ments for the two eyes; these are useless for the bird-watcher. 

 Some form of simultaneous adjustment is necessary, and in many 

 ways the old pattern Goerz-Trieder longitudinally-moving focusing- 

 head was preferable to the transversely-moving heads now in 

 general use. 



A magnification below six diameters is of little use; eight or ten 

 is probably the best for general purposes, although even 12 will give 

 satisfactory results. Besides a binocular, a telescope is often use- 

 ful, especially for the larger and more wary birds. One with an 

 object glass of at least two inches, and a magnification of about 

 25 diameters c^n be highly recommended. The price is compara- 

 tively small, and a little practice is all that is needed to handle it; 

 one soon becomes so proficient that it is easy to follow even Swifts 

 or Swallows in their aerial evolutions. 



The efficiency of both the telescope and binocular can be con- 

 siderably enhanced by a suitable stand. One that I devised for 

 myself consisted of a camera-tripod with a kodak ball-and-socket 

 joint attached ; tliis in its turn screwed on to an apparatus composed 

 of two pieces of wood lined with leather and joined by a long screw 

 which holds the binocular in place. A special heavy ball-and-socket 

 joint is also made by opticians for use with telescopes. By this 

 means the fatigue and strain of holding the glass in place is done 

 away with, and one's hands left free to take notes. ^ 



Before we go any further into the practical details of what to 

 look for and how to look for it, it will be necessary to make what 

 will perhaps appear a long digression on the theoretical side. The 

 main biological problems demanding solution seem to me to be 

 connected with the courtship of birds, and to that subject I shall 

 here confine myself. 



However, as I myself very soon discovered when I began work- 

 ing at the problem of Courtship, to get a real insight into it one 

 must have a working knowledge of the theories of Evolution, the 

 theories of Sex, and the theories of the Animal Mind. On these 

 subjects I must refer the reader to the general works of Darwin, 

 Weismann, Morgan and Washburn cited at the end of this paper. 

 Here I will merely say that all my observations have gone to root 



1 See Huxley ('14), p. 529. 



