BY WAY OF INTRODUCTION 7 



feet. If the observer sank to a depth of nine 

 feet, the circumference of the " .window " would 

 increase to fifty-four feet, and, again, diminish 

 as he came nearer to the surface until it disap- 

 peared altogether. It will be shown how this 

 optical fact enables fish and birds to escape 

 detection from their enemies under the water, 

 as they slip out of the "window," where they 

 are conspicuous as silhouettes against the sky. 



Many of my readers are doubtless familiar 

 with these phenomena, dependent as they are 

 upon optical laws which govern the course of 

 rays of light from air into water, but I have 

 described them at some length for the benefit of 

 those who may be considering the underwater 

 point of view for the first time. 



In the spring number of The Field, May 4th, 

 1912, I published an article on " The Angler 

 from the Fish's Point of View." Consequent 

 upon some statements made, Mr. Cecil Hawkins 

 drew my attention to some errors that are likely 

 to arise in estimating the real position of an 

 object, when viewed from under the water 

 through a plate-glass window, owing to the rays 

 of light from the object under consideration 

 being refracted as they passed through the glass. 



