200 Mr, Morgan's Obfervaiions cmd 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. III. If a jflring*, 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 be moiftened with one of 

 the mineral acids. To the preceding inftance we may add 

 the various inftances of metals which will conduct the eledtri-' 

 cal fluid without any appearance of light, in circumftances 

 the fame with thofe in which the fame force would have ap- 

 peared luminous in pafling through other bodies whofe con- 

 ducting power is lefs. But I proceed to obferve, 



III. That the eafe with which the eledrical fluid is rendered 

 luminous in any particular body is increaled by increafing 

 tiie rarity of the body. The appearance of a fpark, or of 

 the difcharge 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 fa6t ; fimilar phenomena attend the 

 rarefaction of aether, of fplrits of wine, and of water. 



EXP. IV. Intothe orifice of a tube, 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 I filled the tube 

 with quickfilver, 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 lower than it 



* The thicknefs and diameter of the ftring fliould be regulated by the force we 

 employ, 



did 



