TUKE SKY PHENOMENA 7 



Rainbows 

 Even the most honest and experienced observers at times 

 fall into curious errors. The late John Burroughs wrote an 

 interesting article called the "Unapproachable Rainbow" which 

 appeared in the Atlantic Monthly of July, 1920. In it, he effective- 

 ly answered statements made by other correspondents who 

 claimed to have walked or driven through rainbows, as the Toronto 

 writer referred to above did. In so doing, however, he stated 

 that rainbows can not be seen between the hours of nincA.M.and 

 three P.M. This statement is incorrect even for latitudes much 

 south of that in which Mr. Burrough's home was located, but 

 it is especially so for the higher latitudes. On September 30th, 

 1920, I observed a fine bow, almost due North, at 1.15 p. m., 

 and have seen others within the hours mentioned. The physical 

 conditions necessary for the formation of a rainbow are that 

 the sun's (or rarely the moon's) rays shall fall on drops of water, 

 be refracted, then totally reflected on the inside of the drop, 

 then refracted again, emerging at an angle of about 42 degrees 

 from the direction in which they entered. Obviously, these 

 drops may be located anywhere on the arc of a circle whose centre 



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The bow may be seen if the sun is not more than 

 42° above the horizon. 



is in line with the observer's eye and the sun, and which has an 

 angular radius of about 42 degrees. Whenever, then, rain is 

 falling, and the sun is shining, and is not over 42 degs. above the 

 horizon, we may have a rainbow. (Sketch) At the latitude at 



