OF HIGH EEFE AN GIBILITT UPON GASEOUS MATTEE. 
337 
acid in succession. Thus purified it enters the flask F and bubbles through the liquid. 
Charged with vapour it finally passes into the experimental tube, where it is submitted 
to examination. The electric lamp L placed at the end of the experimental tube furnished 
the necessary beam. 
§IV. 
The floating Matter of the A ir. 
Prior to the discovery of the foregoing action, and also during the experiments just 
referred to, the nature of my work compelled me to aim at obtaining experimental tubes 
absolutely clean upon the surface, and absolutely empty within. Neither condition is, 
however, easily attained. 
For however well the tubes might be washed and polished, and how T ever bright and 
pure they might appear in ordinary daylight, the electric beam infallibly revealed signs 
and tokens of dirt. The air was always present, and it was sure to deposit some impu- 
rity. All chemical processes, not conducted in a vacuum, are open to this disturbance. 
When the experimental tube was exhausted it exhibited no trace of floating matter, but 
on admitting the air through the U-tubes containing caustic potash and sulphuric acid, 
a dust-cone more or less distinct was always revealed by the powerfully condensed 
electric beam. 
The floating motes resembled minute particles of liquid which had been carried me- 
