264 



C. S. Cook — Spectrum of Aqueous Vapor. 



humidity. On the other hand it is assumed that if the 

 humidity falls off rapidly vertically there will be little moist- 

 ure in the upper atmosphere. If the spectroscope is a com- 

 petent witness, we must believe that at times no significant 

 amount of vapor exists above the level of a mountain top 



whose sea level altitude is over 0*9 mile, which height for con- 

 venience of discussion we will call a mile. This no doubt no 

 one would call in question. The spectroscope would also lead 

 us to believe that at times there exists at a height greater than 

 one mile such a quantity of vapor that an additional 0*6 of a 

 mile of very damp air is not a significant addition. It is true 

 that in stormy weather observation is difficult, so tfyat the 

 closest work cannot be done ; it is very hard to say how great 

 a proportional part could be easily recognized. Some rough 

 idea of this may perhaps be gained from the diagram dis- 

 played. 



A question of much interest is the effect of the passage of 

 light through clouds. It is certain that the optical effect of 



