124 FRAGMENTS OF SCIENCE 



appear yellowish. But as the sun sinks toward the hori- 

 zon the atmospheric distances increase, and consequently 

 the number of the scattering particles. They abstract in 

 succession the violet, the indigo, the blue, and even dis- 

 turb the proportions of green. The transmitted light un- 

 der such circumstances must pass from yellow through 

 orange to red. This also is exactly what we find in nat- 

 ure. 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 sus- 

 pension 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 phe- 

 nomena, 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 coarseness 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. Professor 

 Briicke has given us the proportions which produce par- 

 ticles particularly suited to our present purpose. One 



