148 ME. &ASSIOT ON THE STEATIEICATIONS IN ELECTEICAL DISCHARGES. 
stratified discharge becomes visible, and as the cai-bonic acid is absorbed by the potash, 
the stratifications gradually appear more clearly defined. I have obtained clearly de- 
fined stratifications when a little moisture was perceptible in the tube, this moisture 
probably assisting the absorption of the carbonic acid by the caustic potas^a , as the 
stratifications gradually become more distinct and diiided, they assume a conical form, 
and lastly the cloud-like appearance (64) of the best mercurial vacua ; after this, under 
some conditions, the stratified appearance of the discharge will enthely cease, the 
whole length of the tube being filled with faint luminosity; when in this state, if the 
outside of the tube is touched by the finger, pungent electrical discharges arise, and 
sparks one-eighth of an inch in length can be elicited. On testing this discharge b) a 
magnet, it will divide in a similar manner to the discharge when taken from a single 
wire ; on continuing the discharges, the peculiar blue phosphorescence previously noticed 
at the negative (68) is often perceivable at both terminals (87) ; and when m this state, if 
a galvanometer is introduced in the circuit, the needle is not deflected, proving that the 
discharge is not continuous but reciprocating ; but if during the discharges the potash 
in the tube is heated, the stratifications become perceptible, and the needle of the 
galvanometer will be deflected, showing that a continuous discharge is now present : this 
experiment is fully described in another part of this paper (88). 
85. I have often found it difficult, and at times impracticable, to obtain precisely 
the same results in carbonic-acid vacua ; they are probably modified, not only by the 
relative purity of the gas and of the potash, but also by the quantity of moisture. 
When the gas was passed through chloride of calcium or through strong sulphuric acid, 
the stratifications appeared more quickly. When moisture had been puiposel) added, 
as by placing a piece of asbestos moistened with boiled distilled water within the tube, 
the cloud-like stratifications were not obtained, although the stratifications of the conical 
form were remarkably clear : in a vacuum-tube thus prepared. No. 61, the caustic potash 
remains in the centre, the asbestos being placed in the narrow end; the potash has 
absorbed the moisture, leaving the asbestos to all appearance perfectly dry. The potash 
in this tube has been repeatedly heated; when heat is applied the stratifications at first 
become clearer; they gradually lose the conical form and become nai-rovv. As the 
heat continues, all trace of stratifications or discharges over the potash is destroyed, that 
portion nearest the negative is blackened (possibly by carbon being evolved). If the 
tube is permitted to cool, the stratifications gradually reappear, until they resume their 
normal state ; on carefully examining the potash, a minute hole is observable in the end 
of it nearest the positive wire, apparently showing a dhection of force in the discharge. 
On Non-conducting Vacua. 
86. I have stated that under certain conditions the stratifications entirely disappeared, 
and as this result is, I believe, new, and has been confirmed by three separate experi- 
ments, I will briefly describe two as they are entered in my note-book. On the 12th ot 
June, two tubes were prepared in the laboratory ot St. Bartholomew s Hospital; in each, 
exclusive of the caustic potash, some fused chloride of calcium was introduced ; m addi- 
