Mr. J. P. Gassiot on Stratificationsin Electrical Discharges. 433 



hours in the experiment, and in this manner the preceding results 

 were obtained. 



In the best TorricelUan vacua the author has been able to obtain, 

 the stratifications always assumed a long cloud-like appearance ; by 

 using ten cells, he on one occasion observed distinct sets of stratifi- 

 cations, one from each terminal, in opposite directions. 



From a variety of experiments made in the laboratory of the 

 Hoyal Institution in temperatures varying from —102° to upwards of 

 4- 600° Fahr., he obtained the following results : — 



"When the flame of a spirit-lamp is applied to the discharge in a 

 vacuum-tube, the stratifications, if they are narrow, will become clearer 

 and divided, attaching themselves to the warmer portion of the tube ; 

 if a section of the tube is heated, the stratifications in that section 

 will be more separated, becoming closer in the cooler portion. 



If heat is applied to a tube which shows the cloud-like stratifica- 

 tions, they will lose their clear distinctness ; the deposit from the 

 negative wire appears to be more free, and distinct sparks or dis- 

 charges are apparent, but none from the positive. 



In a Torricellian vacuum from which the mercury was withdrawn, 

 which gave clear cloud-like stratifications, no change could be ob- 

 served when the temperature was lowered to 4-32° Fahr. ; at a tempe- 

 rature of —102°, all trace of the stratified discharge was destroyed, 

 and in this state the red or heated appearance of the negative wire 

 disappeared, the discharge filling the entire vacuum with a white 

 luminous glow ; on the temperature being raised the stratifications 

 reappear. When the mercury in a Torricellian vacuum is boiled, 

 indicating a heat of upwards of + 600°, the stratifications are also 

 destroyed ; but in this case the mercury as it condenses carries the 

 discharge, becoming a conductor. 



When the mercury is frozen the stratifications disappear, and the 

 discharge did not then illuminate the entire length of the tube ; on 

 presenting a magnet near the tube, the cloud-like stratifications im- 

 mediately reappear from the positive terminal, very distinct, but not 

 so clearly separated as when the tube is in its normal state of tem- 

 perature. 



The author being desirous to obtain vacua free from all trace of the 

 vapour of mercury, endeavoured to do so by means of fusible metal, 

 but traces of air were perceptible ; he also prepared apparatus for a 

 tin vacuum : in a vacuum obtained by means of oxygen and sodium, 

 very good stratifications were observable. At the suggestion and 

 with the assistance of Dr. Frankland, vacua were obtained by ab- 

 sorbing rarefied carbonic acid by means of caustic potassa. This 

 process is described, and a drawing of the apparatus is given. 



In carbonic acid vacua the discharge at first appears in the form 

 of a wavy line ; it is strongly affected on the aj)proach of a magnet 

 or by the hand, but does not generally present the stratified ap- 

 pearance ; if this be present, it is only near the positive terminal : 

 sometimes in the course of a few minutes, but often not until after 

 several days, stratifications are visible, which, as the carbonic acid 

 becomes absorbed, increase ; they subsequently assume a conical 



Phil. May. S. 4. Vol. 17. No. IIG. June 1859. 2 G 



