22 PHOTOGRAPHY FOR BIRD-LOVERS. 



It seems to catch every ray on its highly convex 

 surface and forms a shining line of connection 

 between the camera and its hidden owner. Prob- 

 ably the latter, knowing its purpose, is more 

 conscious of it than there is need to be, but if a 

 dull, or matt-surfaced line is used it will at least 

 save him much anxiety. That birds do on occasion 

 notice and take exception to the line has several 

 times come within my experience, an incident of 

 this kind being mentioned on page 63, and, there- 

 fore, when the distance is not too great the 

 pneumatic release is to be much preferred. Its 

 tubing can easily be covered over with leaves, sand 

 or earth, or buried in the grass. In theory, of 

 course, there is no reason why it should not be 

 serviceable in any length, but, as we have said, in 

 practice its usefulness will be found rapidly to 

 diminish after some fifty or sixty feet are put into 

 operation. The ball, too, for such lengths is 

 bulky, but the chief drawback is the slowness of its 

 working. The expansion of the rubber tube 

 under pressure allows a small quantity of air to 

 be squeezed from the ball without exerting much 

 force in the teat, and a much greater and more 

 serious cause of this loss of, or delay in, working 

 pressure is the compressibility of air. Twenty 

 times the amount of air necessary to fill the teat 

 may be squeezed from the ball into a long length of 



