252 FRAGMENTS OF SCIENCE. 



The experimental tube now before you contains a 

 quantity of a different vapor from that which we have 

 hitherto employed. The liquid from which this vapor is 

 derived is called the nitrite of butyl. On sending the elec- 

 tric beam through the vapor, which has been carried in by 

 air, the chemical action is insensible. I add to the vapor a 

 quantity of air which has been permitted to bubble through 

 hydrochloric acid. "When the beam is now turned on, so 

 rapid is the action and so dense the clouds precipitated, 

 that you could hardly, by an effort of attention, observe the 

 dark interval which preceded the precipitation of the cloud. 

 This enormous augmentation of the action is due to the 

 presence of the hydrochloric acid. Like the chlorophyl in 

 the leaves of plants, it takes advantage of the loosening of 

 the molecules of nitrite of butyl by the waves of the electric 

 light. 



In these experiments we have employed a luminous 

 beam for two different purposes. A small portion of it has 

 been devoted to the decomposition of our vapors, while the 

 great body of the light has served to render luminous the 

 clouds resulting from the decomposition. It is possible to 

 impart to these clouds any required degree of tenuity, for 

 it is in our power to limit at pleasure the amount of vapor 

 in our experimental tube. When the quantity is duly 

 limited, the precipitated particles are at first inconceivably 

 small, defying the highest microscopic power to bring them 

 within the range of vision. Probably their diameters might 

 then be expressed in millionths of an inch. They grow 

 gradually, and as they augment in size they scatter a con- 

 tinually increasing quantity of wave-motion, until finally 

 the cloud which they form becomes so luminous as to fill 

 this theatre with light. During the growth of the particles 

 the most splendid iridescences are often exhibited. Such 

 I have sometimes seen with delight and wonder in the 

 atmosphere of the Alps, but never any thing so gorgeous 



