2o 6 Mr. Morgan's Obfervatiom and Experiments on 
brilliantly over the’ inflde of a tube, merely by fpreading fome 
pitch very thinly over the outfide of the fame tube. 
EXP. xiii. I would now give another fact, whofe Angulari- 
ties depend very much on the influence of the medium through 
which the electrical light is made to pafs. If into a Torricel- 
lian vacuum, of any length, a few drops of aether are conveyed, 
and both ends of the vacuum are flopped up with metallic con- 
ductors, fo that a fpark may pafs through it, the {park in its 
paflage will a {fume the following appearances. When the eye 
is placed clofe to the tube, the fpark will appear perfedly 
white. If the eye is removed to the diftance of two yards, it 
will appear green ; but at the diftance of fix or feven yards, 
the colour of the fpark will be reddifh. Thefe changes evi- 
dently depend on the quantity of medium through which the 
the light pafles ; and the red light more particularly, which 
we fee at the greateft diftance from the tube, is accounted for 
on the fame principle as the red light of a diltant candle or a 
beclouded fun. 
exp. xiv. Dr. Priestley long ago obferved the red ap- 
pearance of the fpark when pafting through inflammable air. 
But this appearance is very much diverftfied by the quantity of 
medium, through which you look at the fpark. When at a 
very confiderable diftance, the red comes to the eye unmixed; 
but, if the eye is placed clofe to the tube, the fpark appears 
white and brilliant. In confirmation, however, of fome of 
my conclufions, I would obferve, that by increaftng the 
quantity of fluid which is conveyed through any portion 
of inflammable air, or by condenfmg that air, the fpark may 
be entirely deprived of its red appearance, and made perfectly 
brilliant. I have only to add, that all weak explofions and 
fpark s, 
