146 ME. GASSIOT ON THE STEATIFICATIONS IN ELECTEICAl DISCHARGES, 
at b ; the negative terminal a, from its form concentrating the blue-tongue dischar,,e on 
the upper surface of the tube, where it impinged, foiming an oval-shaped spot remar - 
ably rich in the fluorescent blue rays. This iUummated spot could be lepelle oi 
attracted, concentrated or difSlsed, according to the direction m which the magnet was 
presented. On removing the ether from a, and aUowing the mercuiT to liquefy, a 
tremulous motion was purposely imparted to the mercury, while at I it remamed i^d 
when kept frozen. By these means a vibrating or oscillating motion was impaite to 
the blue-tongue discharge, as it impinged on the glass; this discharge appealing as a 
focus of light, its form being regulated by that which the negative termmal — 
81. From these experiments in temperatures through a range of upwaids ot i 
Fahe., I obtained the following results ; — ■, i j 
In a Torricellian vacuum which gave good clouddike stratifications, no change co^d 
be observed when the temperature was lowered to fi- 32° ; but at a temperatme of 
all traces of stratifications were destroyed, and in this state the red or heated appearance 
of the negative wire disappeared, the discharge filHng the entne vacuum with a u te 
luminous glow ; on the temperature being raised by the application of heat to the mer- 
cury, the stratifications reappeared. When the mercury was boiled, mdicatmg heat ol 
upwards +600°, the stratifications were all destroyed, but in this case the dischaige 
passed along the mercury as it condensed in the cooler portion of the tube. ^^Tien t le 
mercury was frozen the stratifications disappeared, and the discharge did not illumiiiate 
the entire length of the tube, but merely the terminals ; in this state, when a horseshoe 
magnet was brought near the tube, the cloud-like stratifications immediately appeared 
from the positive wire very distinct and large, but not so clearly separated as when the 
tube was at its normal temperature. 
On Vacua free from Vapour of Mercury. 
82. I was desirous to obtain a vacuum, if possible, more perfect, and particulaih one 
free from any trace of mercury. In those with which I had to this time expenmenteL . 
I believe the only medium remaining in the tube was mercurial vapoiu’, oi la abcei 
tained that the slightest trace of air altered the colour of the stratifications, and oiim 
by using the process suggested by Mr. Welsh, I had obtained precisely the same le&v t 
whether the tubes were previously filled with air, hydrogen, or oxygen. In t le expeii 
ments hitherto described in this, as well as in my former communication, I had obtained 
the best results by filling carefully prepared glass tubes with pure mercury, and t ms 
forming good Tonicellian vacua. Such vacua necessarily contain mercury in a state o 
vapour, and I assumed that the stratifications observable when electrical discharges are 
taken in such vacua, were “ probably due to the pulsations or impulses of a force acting 
on this highly attenuated but resisting medium In a perfect vacuum all the e ect ue 
to such assumed resistance ought to be removed, and I anticipated that the discharge 
would either not pass from wire to wire, or it might pass in some other form t lan t la 
* Philosopliical Transactions, Part I. p. Ifi 18o8. 
