2o6 Mr. Morgan's ObfervatJons and Experiments on 



brilliantly over the infide of a tube, merely by fpreading fome. 

 pitch VQvy thinly over the outfide of the fame tube. 



EXP. XIII. I would now give another fa6l, whofe Angulari- 

 ties depend very much on the influence Oi the medium through 

 which the eletftrical 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 (lopped up with metallic con- 

 dudlors, fo that a fpark may pafs through it, the fpark in its 

 paflage will affume the following appearances. When the eye 

 is placed clofe to the tube, the Ipark will appear perfe6lly 

 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 reddifli. Thefe changes evi- 

 dently depend on the quantity of medium through which the 

 the light paiies ; and the red light mxore particularly, which 

 we fee at the greatefl: diftance from the tube, is accounted for 

 on the fame principle as the red light of a didant candle or a 

 beclouded fun. 



EXP. XIV. Dr. Priestley long ago obferved the red ap- 

 pearance of the fpark when paffing through inflammable air. 

 But this appearance is very much diverfified 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 j 

 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 Vv^ould obferve, that by increafing *the 

 quantity of fluid which is conveyed through any portion 

 of inflammable air, or by condenfing that air, the fpark may 

 be entirely deprived of its red appearance, and made perfedly 

 brilliant. I have only to add, that all weak explofions and 



fparks, 



