THE MICROSCOPIC PLANT AND ANIMAL 

 WORLD IN ULTRAVIOLET LIGHT 



By Florence E. Mkiek, 



Research Associate, Division of Radiation and, Orgatilims, 



Smithsonian Institution 



[With 1 plate] 



The spectrum, seven beautiful colors — red, orange, yellow, green, 

 blue, indigo, and violet — has always been familiar to mankind as a 

 rainbow in the cloud or in the dew upon the grass, but it was not 

 until the seventeenth century that the analysis and synthesis was 

 made of these colors. In the early part of that century, Father 

 Grimaldi, an Italian Jesuit physicist, discovered the foundation of 

 one of the methods of producing the spectrum. Purely by chance 

 he placed a hair in front of a tiny hole through which a sunbeam 

 penetrated his dark cell. He was astonished to see that the hair 

 projected a shadow much larger than his own. He measured both 

 shadows before he would believe his eyes were observing an actual 

 fact. Then he made repeated trials in various ways, with always 

 the same result. Finally, convinced of the truth of his accidental 

 observation, he gave the name of diffraction to the deviation of rays 

 of light from a straight source when they graze the surface of an 

 obstacle. This property is used in the diffraction grating for 

 the spectrum. 



Father Grimaldi also observed with admiration the splendor of 

 colors resulting from the passage of light through a prism, but he 

 did not make any scientific study of them. 



It was after Father Grimaldi's death in the same century that 

 Sir Isaac Newton, then a keen young scholar at Cambridge, with the 

 attention to details that leads to great discoveries, mused over the 

 same live, brilliant colors cast on a screen in a dark room by a ray 

 of sunlight passing through a prism. Each ray, distinct in its 

 color, is also distinct in its refrangibility or bending. Newton 

 saw that it was not the glass prism that communicated splendor to 

 the ray of sunlight. The seven colors were invisibly united in white 

 light; the prism separating them one from the other made them 

 visible. By placing screens conveniently, Newton could study each 



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