﻿242 Prof. Tyndall on Comeiary Theory. 



bit of bibulous paper, rolled it up into a pellet not the fourth 

 part of the size of a small pea, and moistened it with a liquid 

 possessing a higher boiling-point than that of water. I held the 

 pellet in my fingers until it had become almost dry, then intro- 

 duced it into a connecting-piece and allowed dry air to pass over it 

 into this tube. The air charged with the modicum of vapour thus 

 taken up was subjected to the action of light. A blue actinic 

 cloud began to form immediately, and in five minutes the blue 

 colour had extended quite through the experimental tube. For 

 some minutes this cloud continued blue, and could be completely 

 quenched by a NicoFs prism, no trace of its light reaching the 

 eye when the Nicol was in its proper position. But its particles 

 augmented gradually in magnitude, and at the end of fifteen mi- 

 nutes a dense white cloud filled the tube. Considering the 

 amount of the vapour carried in by the air, the appearance of a 

 cloud so massive and luminous seemed like the creation of a 

 world out of nothing. 



" But this is not all ; the pellet of bibulous paper was removed, 

 and the experimental tube was cleared out by sweeping a current 

 of dry air through it. This current passed also through the con- 

 necting-piece in which the pellet of bibulous paper had rested. The 

 air was at length cut off and the experimental tube exhausted. 

 Fifteen inches of hydrochloric acid were then sent into the tube 

 through the same connecting-piece. Now it is here to be noted 

 (1) that the total quantity of liquid absorbed by the pellet in 

 the first instance was exceedingly small, (2) that nearly the 

 whole of this small quantity had been allowed to evaporate be- 

 tween my fingers before the pellet was placed in the connecting- 

 piece, (3) that the pellet had been ejected and the tube in 

 which it rested rendered for some minutes the conduit of a 

 strong current of pure air. It was part of such a residue as 

 could linger in the connecting-piece after this process, that was 

 carried into the experimental tube by the hydrochloric acid and 

 subjected there to the action of light. 



" One minute after the ignition of the electric lamp a faint 

 cloud showed itself; in two minutes it had filled all the anterior 

 portion of the tube and stretched a considerable way down it ; it 

 developed itself afterwards into a very beautiful cloud-figure; 

 and at the end of fifteen minutes the body of light discharged by 

 the cloud, considering the amount of matter involved in its pro- 

 duction, was simply astounding. But though thus luminous, 

 the cloud was far too fine to dim in any appreciable degree ob- 

 jects placed behind it. The flame of a candle seemed no more 

 affected by it than it would be by a vacuum. Placing a page of 

 print so that it might be illuminated by the cloud itself, it could 

 be read through the cloud without any sensible enfeeblement. 



