of Electricity. lOy 



a quantity of the fluid residing in the substance to which it 

 is presented, and to drive it oft' into the earth, in the same 

 manner as the fluid m an insulated conductor is repelled 

 from the nearest to the remotest end by the action of a 

 machine, as we have attempted to prove under the second 

 proposition : in this situation the substance mentioned will 

 have less than its natural share, and of course indicate ne- 

 gative electricity. If we reverse the picture, the excited 

 wax, by its opposite qualities, enables the substance to re- 

 ceive from the earth an additional quantity, which under 

 insulation appears in the form of positive electricitv. 



The seventh proposition assumes an universal and uniform 

 distinction between the two states of electricity. If no 

 means are discoverable by which these states can be ascer- 

 tained, it is sufficiently obvious that all reasoning respect- 

 ing their particular situations and circumstances must be 

 vagiie and nugatory : the certainty and facility of this di- 

 stinction is an essential prop to the whole theory ; let us 

 therefore examine evidence. The proofs of this distinction 

 arc referable to two classes : one derived from the appearances 

 of electric light ; the other from the pha^nomena of attraction 

 and repulsion. If a point be presented to the insulated 

 rubber of a machine, which by Proposition 5. receives the 

 fluid from such point, a diverging huuinous stream will 

 become apparent, which resembles a pencil of rays centring 

 at the point, and darting through the air towards the rubber 

 with a crackling noise, conformably to the expectations we 

 should form of the emission of a fluid resisted equally in its 

 motion by the surrounding atmosphere : but if the needle 

 be transferred in contact with the rubber, its point out- 

 wards, which by Proposition 3. then becomes the recipient 

 instead of emitting the electric fluid, the appearance will 

 be changed : when the fluid is collected from the circum-> 

 jacent air towards a point, it is natural to conceive it slowly 

 and invisibly ])ercolating from all parts in an equal propor- 

 tion, till it approaches sufficiently near to break through the 

 intermediate space ; and as this space will be equal on every 

 aide, the negative electricity will become visible in the form 

 of a steadv, luminous globule on the point, accompanied 

 with little noise : and this is consonant with experience. 

 The difilrent efl'ects of the two electricities may be advan- 

 tageously observed by receiving the stream upon the flat 

 i'ide of a piece of paper : a strong |)lus stream forms a beau- 

 tiful star about four inches in diameter, consisting of very 

 distinct radii not ramified ; the minus stream forms no star, 

 while manv pointed brushes centre towards the paper (Ca- 



vallo). 



