Sir Humphry Davy on Electrical Phenomena in Vacuo. SS7 
eluded, that such a vacuum prevented the charging of coated 
glass. 
The existence of mercurial vapour in the most complete to- 
ricellian vacuum, induced Sir Humphry Davy to doubt the ac- 
curacy of these deductions, and he was therefore led to put 
them to the test of experiment, by forming the vacuum with a 
comparatively fixed metal in fusion. 
The apparatus which he used for 
this purpose, consists of a curved 
glass tube AD, having one of its 
legs A closed, and longer than the 
other. In the closed leg CA, a 
wire of platinum B was hermeti- 
cally cemented, in order to trans- 
mit the electricity ; and for the 
purpose of ascertaining the power 
of the vacuum to receive a charge, 
a small cylinder of metallic foil E 
was placed as a cap, on tubes that 
had not the wire B. ' When the closed leg had been filled with 
mercury, or fused tin, whose surface stood at C, the open end D 
was exhausted by the stopcock F, connected by the moveable 
tube G, with an excellent air-pump, and to ensure greater 
accuracy, the exhaustion was made after the tube and apparatus 
were filled with hydrogen by means of the stop-cock F. 
By the aid of this apparatus, in which the rarified air or 
gas could be made to balance a column of fluid metal of any 
length from g^oth of an inch to 20 inches. Sir Humphry Davy 
could easily procure a vacuum either of a large or a small size ; 
and by using recently distilled quicksilver, and boiling it in va- 
cuo, six or seven times, from the top to the bottom, and from 
the bottom to the top of the tube, and making it vibrate re- 
peatedly, by striking it with a small piece of wood, he obtained 
a column in the tube free from the smallest particle of air. 
The vacuum being thus rendered perfect. Sir Humphry found 
that in every case the mercurial vacuum was permeable to elec- 
tricity, and could be rendered luminous either by the common 
spark, or by the shock from a Leyden jar, the coated glass be- 
coming charged. The intensity, however^ of these effects, was 
