1 8 PHYSICAL SCIENCE BK. i 



do the two alleged colours, light and shade, do in 

 a case of this kind, when the presence of an endless 

 variety must be accounted for ? Again, 



certain authorities are of opinion that the following 

 is the method of formation of the rainbow : In the 

 quarter of the sky where rain is falling, they say, 

 the drops of falling rain are so many mirrors ; 

 from each mirror, therefore, is reflected an image 

 of the sun. By and by, many, in fact, countless, 

 images, descending and crossing abruptly, are all 

 blended together. Therefore the rainbow is just a 

 blending of a great number of images of the sun. 



6 They appeal to the following argument in proof of 

 this : On a clear day, say they, set out a thousand 

 basins, and they will all contain images of the 

 sun. Or arrange single drops of water on single 

 leaves ; they will each have an image of the sun. 

 On the other hand, an immense pond will have no 

 more than one image. Why so ? Just because 

 every smooth surface that is fenced off, and sur 

 rounded by its own boundaries, is a mirror. Again, 

 divide a pond of very large size into several small 

 ponds by inserting partition walls ; it will show as 

 many images of the sun as it has divisions. Leave 

 it as it was, spreading out to its full extent, and it 



7 will show but one reflection of him. The small 

 extent of the liquid or pond makes no manner of 

 difference. If the surface is circumscribed, it forms 

 a mirror. Well then, those countless drops, which 

 are carried down by a falling shower, are so many 

 mirrors, and contain so many reflections of the sun. 

 To an observer right in front of them they 

 present the appearance of being mixed up : the 

 intervals which part them from each other are not 

 distinguished, their mere distance from the observer 



