■2oo Mr. Morgan’s Obfervations mid Experiments on 
drops of either of the mineral acids are poured, it will be 
almoft impoffible to make the fluid luminous in Its paflage 
through the tube. 
exp. in. If a {Iring*, whofe diameter is one- eighth of an 
inch and whofe length is fix or eight inches, is moiftened with 
water, the contents of a jar will pafs through it luminoufly, 
but no fuch appearance can be produced by any charge of the 
fame jar, provided the fame firing he moiftened with one of 
the mineral acids. To the preceding inftance we may add 
the various inftances of metals which will conduT the electri- 
cal fluid without any appearance of light, in circumftances 
the fame with thofe in which the fame force would have ap- 
peared luminous in palling through other 'bodies whofe con- 
ducting power is lefts. But I proceed to obferve, 
III. That the eafe with which the eleCtrical fluid is rendered 
luminous in any particular body is increafed by increafing 
the rarity of the body. The appearance of a fpark, or of 
the difeharge of a Leyden phial, in rarefied air "is well known. 
But we need not reft the truth of the preceding obfervation on 
the feveral varieties' of this fad ; fimilar phenomena attend the 
rarefadion of aether, of fpirits of wine, and of water. 
exp. iv. Into the orifice of atube, 48 inches long, and two- 
thirds of an inch in diameter, I cemented an iron ball, fo as to 
bear the weight which prefled upon it when ! filled the tube 
with quickfiilver, leaving only an interval at the open end, 
which contained a few drops of -water. Having inverted the 
tube, and plunged the open end of it into a bafon of mercury, 
the mercury in the tube flood nearly half an inch rower than it 
* The thicknefs and diameter of the iking fliould be regulated by the force we 
employ. 
did 
