432 FRAGMENTS OF SCIENCE. 



to keep constantly before us the physical images which 

 underlie our terms. Therefore I say, sharply and defi- 

 nitely, that the components of the molecules of sulphurous 

 acid are shaken asunder by the ether-waves. Enclosing 

 sulphurous acid in a suitable vessel, placing it in a dark 

 room, and sending through it a powerful beam of light, we 

 at first see nothing: the vessel containing the gas seems as 

 empty as a vacuum. Soon, however, along the track of the 

 beam a beautiful sky-blue color is observed, which is due 

 to light scattered by the liberated particles of sulphur. 

 For a time the blue grows more intense; it then becomes 

 whitish; and ends in a more or less perfect white. When 

 the action is continued long enough, the tube is filled with 

 a dense cloud of sulphur particles, which by the application 

 of proper means may be rendered individually visible.* 



Here, then, our ether- waves untie the bond of chemical 

 affinity, and liberate a body sulphur which at ordinary 

 temperatures is a solid, and which therefore soon becomes 

 an object of the senses. We have first of all the free atoms 

 of sulphur, which are incompetent to stir the retina 

 sensibly with scattered light. But these atoms gradually 

 coalesce and form particles., which grow larger by continual 

 accretion, until after a minute or two they appear as sky- 

 matter. In this condition they are individually invisible; 

 but collectively they send an amount of wave-motion to the 

 retina, sufficient to produce the firmamental blue. The 

 particles continue, or may be caused to continue, in this 

 condition for a considerable time, during which no micro- 

 scope can cope with them. But they grow slowly larger, 

 and pass by insensible gradations into the state of cloud, 

 when they can no longer elude the armed eye. Thus, 

 without solution of continuity, we start with matter in the 

 atom, and end with matter in the mass; sky-matter being 

 the middle term of the series of transformations. 



Instead of sulphurous acid, we might choose a dozen 

 other substances, and produce the same effect with all of 

 them. In the case of some probably in the case of all it 

 is possible to preserve matter in the firmamental condition 



* M. Morren was mistaken in supposing that a modicum of sulphur- 

 ous acid, in the drying tubes, had any share in the production of the 

 " actinic clouds " described by me. A beautiful case of molecular 

 instability in the presence of light is furnished by peroxide of 

 chlorine as proved by Professor Devvar. 1878. 



