264 ( So ) 



mitted light under such circumstances must pass from 

 yellow through orange to red. 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 tur- 

 bid by the mechanical suspension of exceedingly small 

 foreign particles. 



Here, as before, we encounter our skeptical "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, Can small 

 particles be really proved to act in the manner indicated ? 

 No doubt of it. Each one of you can submit the ques- 

 tion to an experimental test. Water will not dissolve 

 resin, but spirit will, and when spirit which holds 

 resin in solution is dropped into water the resin imme- 

 diately separates in solid particles, whicli render the 

 water milky. The coarseness of this precipitate de- 

 pends on the quantity of the dissolved resin. You can 

 cause it to separate in thick clots or in exceedingly fine 

 particles. Professor Briicke has given us the propor- 

 tions which produce particles particularly suited to our 

 present purpose. One gramme of clean mastic is dis- 

 solved 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 exceed- 

 ingly fine precipitate is thus formed, which declares its 



