116 FEAGMENTS &F SCIENCE. 



This also is exactly what we find in nature. Thus, 

 while the reflected light gives us at noon the deep azure 

 of the Alpine skies, the transmitted light gives us at 

 sunset the warm crimson of the Alpine snows. The 

 phenomena certainly occur as if our atmosphere were a 

 medium rendered slightly turbid by the mechanical 

 suspension of exceedingly small foreign particles. 



Here, as before, we encounter our sceptical ' as if.' 

 It is one of the parasites of science, ever at hand, and 

 ready to plant itself and sprout, if it can, on the weak 

 points of our philosophy. But a strong constitution 

 defies the parasite, and in our case, as we question the 

 phenomena, probability grows like growing health, 

 until in the end the malady of doubt is completely 

 extirpated. The first question that naturally arises is 

 this: Can small particles be really proved to act in the 

 manner indicated? No doubt of it. Each one of you 

 can submit the question to an experimental test. 

 Water will not dissolve resin, but spirit will dissolve 

 it; and when spirit holding resin in solution is dropped 

 into water, the resin immediately separates in solid 

 particles, which render the water milky. The coarse- 

 ness of this precipitate depends on the quantity of the 

 dissolved resin. You can cause it to separate either 

 in thick clots or in exceedingly fine particles. Pro- 

 fessor Briicke has given us the proportions which pro- 

 duce particles particularly suited to our present 

 purpose. One gramme of clean mastic is dissolved in 

 eighty-seven grammes of absolute alcohol, and the 

 transparent solution is allowed to drop into a beaker 

 containing clear water, kept briskly stirred. An ex- 

 ceedingly fine precipitate is thus formed, which de- 

 clares its presence by its action upon light. Placing a 

 dark surface behind the beaker, and permitting the 

 light to fall into it from the top or front, the medium 



