,jo Oiferv.ii'icnt and Iii/emiees refpeSling CunhiiJIioH. 



convexity of the metal cup, where it is again condenfed by the fuperior comluaing power 

 of the m.nal to that of water, and -.vhere, if it be in due quantity, and of fulhcient denfity, 

 it manifefts itfclf by a fpark, and infallibly again decompounds water : hence bubbles are 

 feen to rife from the end of the lower wire, and from the metal cup, as well as from the 

 point of the upper wire. 



From thefe interpretations it will not be dKhcult to explain the rcafon of a fpark appear- 

 ing in feme cafes at the points of both the upper and under wire ; why in other cafes h 

 ap^pears at the point of the upper wire only, why in others it appears at the point of t!:c 

 lower wire only -, namely, according to the denfity of the fire of the difcharge there ac- 

 cumulated. 



Concerning the agency of elearical fire in cauHng the hydrogen and oxygen g;iz of the 

 fuppcfed decompounded water to undergo combuftion and produce water, it is well 

 known that the fmalleft vifible fpark, or particle of flame, or fire, can kiiulle as r.ipidly a 

 very large quantity of hydrogen and oxygen ga/, as the grcaicft quantity of flame, fparks, 

 or fire, can kindle the fmalleft quantity of thefe two gazes -, while, on the other hand, the 

 lar^eft mafs of matter, heated moft intenfely, but (hort of ignition, cannot produce com- 

 buftion of oxygen and hydrogen gaz. 



Although, as hath been above explained, calorjc and light, in a fufficiently denfe ftatc, 

 may decompound every compound fubftance in nature ; it is alfo well afcertained, that 

 caloric, in certain ftates, univerfally promotes chemical combinations. The mode of agency, 

 in this latter cafe, I apprehend to be in a difterent way from that commonly accepted -, for 

 1 think it is unneceflary to fuppofe that it operates by increafing the power of chemical at- 

 traaion, and I conceive its agency to be merely diminifiilng or deftroying the powers which 

 counteraa cliemical union ; efpecially diminilliing cohefive attraaion, and exciting motion 

 aiiong the particles of the different fubftanees : hence thefe fubftances are applied to one 

 another, within their fpheres of chemical attraaion ; or the chemical attraaion acts be- 

 t.veen a greater number of points of the different bodies, as when caloric renders folids and 

 intlatlic fluids into the elaftic fluid ftate. 



Accordingly, when an elearic fpark, or the fmalleft particle of flame, or of an ignited 

 fubftance, is applied to the gaz produced in the above procefs, or to the mixture of hydro- 

 gen and oxygen gaz, the ultimate particles of thefe gazes neareft to the flame are driven 

 from it in all direaions, as from a centre, by the interpofition of fire, or of caloric and light ; 

 fo that they are brought within the fphere of their chemical attraaion for the ultimate 

 particles of the gazes at'a certain diftance from the centre of application of fire; which 

 therefore unite, and the caloric and light, difengaged by that union, aa in a fimilar manner 

 in producing union among the next fet in order of proximity, of the ultimate particles of 

 the gazes ; the difengaged caloric and light of which aa in producing union of the next 

 fet of ultimate particles in order ; and fo on fucceffively, but with incalculable velocity, the 

 grcateft bulk of ultimate particles of the two gazes unite with one another; the known 

 prcdjcls of which union are fire and water ; or light, caloric, and water. According to 

 this hypothcfis, if caloric or fire, or merely caloric of fufficicnt intenfity and quantity, be 

 applied to a given bulk of hydrogen and oxygen gaz, no combuftion fiiould be produced ; 

 as the caloric will be interpofed in fuch quantity that all the ultimate particles muft be at 

 the fame inftant driven from one anotlter in all direaion.s, fo that they arc beyond their 



fpheres 



