REFRACTION. 87 



From my own experience in a diving dress in the clear 

 waters of the Torres Straits, which were undisturbed by any 

 ripples, eddies, etc., I found that all objects in the hori- 

 zontal plane were invisible to me beyond a distance of about 

 twenty feet the head of a shark coming towards me would 

 be visible at about seventeen feet, while its tail would at 

 the same time be quite invisible and lost in the misty wall 

 surrounding me. It may be therefore confidently assumed 

 that the wader, even when faced by the trout, will, as far 

 as his waders are concerned, be unnoticed by the trout at 

 a distance of from twenty-five to thirty-five feet. 



I wish to acknowledge the help of my brother Dr. PHILIP EGERTON SHAW, D.Sc. 

 Nottingham College, who assisted me in writing " The Vision of a Trout " and preparing 

 the diagrams. 



