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THE POPULAR SCIENCE MONTHLY. 



no matter what the substance may be of which they are composed, 

 shed forth a pure firmamental blue ; and that from them we can man- 

 ufacture in the laboratory artificial skies which display all the phe- 

 nomena, both of color and polarization, of the real firmament. 



With regard to the production of the green of the spectrum by the 

 overlapping of yellow and blue, Goethe, like a multitude of others, 

 confounded the mixture of blue and yellow lights with that of blue 

 and yellow pigments. This was an error shared by the world at large. 

 But in Goethe's own day, Wiinsch, of Leipsic, who is ridiculed in the 

 " Farbenlehre," had corrected the error, and proved the mixture of blue 

 and yellow lights to produce white. Any doubt that might be enter- 

 tained of Wiinsch's experiments and they are obviously the work 

 of a careful and competent man is entirely removed by the experi- 

 ments of Helmholtz and others in our own day. Thus, to sum up, 

 Goethe's theory, if such it may be called, proves incompetent to ac- 

 count even approximately for the Newtonian spectrum. He refers it to 

 turbid media, but no such media come into play. He fails to account 

 for the passage of yellow into red and of blue into violet ; while his 

 attempt to deduce the green of the spectrum from the mixture of yel- 

 low and blue is contradicted by facts which were extant in his own 

 time. 



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HOW ANIMALS EAT. 



By HERMAN L. FAIRCHILD. 



IN the digestion of the higher animals, the first act is the trituration 

 of the food to assist and hasten its solution. We might term this 

 mechanical digestion, as it is a reduction of the food preparatory to 

 the essential physical and chemical process. Although very simple in 



/ 3 



Pig. 1. Organs op the Mouth in Insects: 1. Trophi of a masticating insect (beetle): a, labrum 

 or upper lip ; b, mandibles ; c, maxillse with their palpi ; d, labium or lower lip with its palpi. 



2. Mouth of a butterfly : o, eye ; /, base of antennae ; g, labial palp ; h, spiral trunk or "antlia " 



3. Mouth of a hemipterous insect {Nepa cinerea) : I, labium ; m, maxillse ; n, mandibles. 



