ELECTRICITY

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than its natural quantity, but in a less proportion than the conti-guous air, am! if the difference of the proportionate quantities besufficiently great, the body will receive part of the fluid troin theair. The* reverse of this 'is also true. The pha-nomenon is pro-duced partly by tire attraction of the contiguous body, and partlyby the<repuisive force of the fluid, (ax. 2,) by which it is propelledtowards the part where it is least resisted.

Cor. From this, according to ax. 5, it follows that bodies emit-ting tin; fluid are electrified positively, and bodies receiving it areelectrified negatively, and vice versa.

Prop. V. When a body is electrified either positively or nega-tively, the bodies which arc near it will be electrified with thecontrary electricity, if the bodies be not insulated. This is a phe-nomenon exhibited in all electrical experiments. The cause hashitherto been reckoned among the desiderata of electricity. Nopha-nomenon in electricity seems to be more difficult to solve,than the question, Why positive electricity induces the negativehind on any body within its sphere of action, and why the nega-tive kind produces the positive in similar circumstances > Mr.Tytler pronounces it totally insolvabie, unless we give up the ideaof accumulation and deficiency of the electric fluid in differentbodies. On Dr. Franklin’s principles no' solution hath been at-tempted. Mr. Cavallo places this among the properties of electri-city, for which he doth not pretend to account, but gives us thecauses of other pha nomena. On the theory here proposed thisdifficulty entirely vanishes, for since when one body is emittingtlic fluid another which is near that body must be receiving it, andvice versL Therefore, (ax. 6, and Prop. IV.) when a body iselectrified the adjacent bodies will be electrified with the contrarypower, till its quantity of fluid bears a certain proportion to thatof the body', by' which it is electrified. Hence, if the body placednear that which is electrified be a conductor, it will continue intiie opposite state.

Prop. VI. Two bodies, at liberty to move in the air, will, whenelectrified either positively or negatively, appear to repel eachother; but when one is positive, and the other negative, they appearto attract each oilier. This is well known to electricians, but thecause of the repulsion of two bodies negatively electrified has notbeen wpll explained. We hope the following will be satisfactory :Let two bodies, as two cork balls, be suspended in the air, and I ,let them be electrified positively : then since they are emitting thefluid there will be a re-ad ion of the air against the fluid which isleaving the bodies, and the air will be driven outward and reactagainst the balls. It is evident that this re-action will be greatestbetween the balls, for since it proceeds from the tw o adjacent sur-faces the air will be impelled or driven outward from both surfaces,and consequently will re-act with a greater force, and thus theKails will be repelled. 2. Let the two balls be electrified nega-tively, then the motion of the fluid towards the balls by its actionon the air will cause a pressure at the surfaces of the "halls on allsides towards the centre, that is, the fluid moving towards the ballswill cause some degree of motion in the air towards them ; andsince this motion is towards both the adjacent surfaces, the forcewill he increased on each, while the opposite sides remain unal-tered, and thus they will be repelled or driven asunder. And hereit may be observed, that the repulsion in positive electricity iscaused by the reaction of the air, which is driven outward, or fromthe balls : but in negative electricity it is occasioned by the actionuf the air, which is driven inward, or towards the balls. Also olherthings being the same, the effect will be greater in positive elec-tricity than in the negative, for that is raused by an excess of fluid,and this by a deficiency of the fluid.. 3. Let one of the bodies beelectr fie 1 positively, and the other negatively; then, at the ad-jacent surfaces, the fluid which is given out Irom one supplies thedeficiency of the other, and thus no motion of the air betweenthem is produced either -inward or outward ; but the forces re-main on the two opposite sides, and therefore the balls will bedriven together, thai. is, they will apparently attract each other,withconsiderable force.

Prop. VII. If an insulated conductor free from points be putwithin a certain distance of ari electrified body, the end presentedw ill he electrified will , the contrary power, am( the more distant endwith the same power. This appearance is oi .ervetl by all elec-tricians, out no good reason has been assigned for it. We offerthe following on the principles above laid down. Let the body,

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to which the insulated conductor is presented, be electrified posi-tively, then the contiguous air is receiving the fluid, and since theair is,an electric the atmospheres of fluid on the particles of the airwill extendon the more distant sides of the particles, as explainedin Propositions f and 6, and in like manner will the end of the pre-sented conductor be influenced, but because of its w eak attractionfor (lie fluid, its particles cannot retain the almoqdiere on theirmore distant sides, andthusit is conducted to the further end whereit affects the particles of l^ie contiguous air by its endeavour to es-cape ; and thus the nearer end is negative and the other positive.The etfect is contrary if the body, to which it is presented, be ne-gative. This also accounts for the effects ofllie electrophorus.

Pnor. V1II. If one side of the I.eyden phial, or of a thin plate ofcoated glass, be presented to a conductor electrified positively, andif the other side communicate by conductors with the earth, theglass w ill become strongly charged, and if the two coatings be thenconnected by a conductor an explosion will take place. Thiscurious pha-nomenon may be fhus explained. Because the coat-ing is a conductor, as it receives the fluid, it disperses it over thecoated surface, and the particles of glass at this coating obtain anadditional dose of the fluid by which the atmospheres of fluid onthe next particles stand n ore to the other side, ami thus, if thefluid on the positive conductor be sufficiently intense, and the glassvery thin, tiie particles at the other coating will be affected, andsince this coaling is a conductor and communicates with the earth,the atmosphere propelled to tins side will be carried otf, and thusthe pressure or resistance is partly removed from the side whiph isreceiving the fluid ; so that it will receive still more, and also morewill be carried away from the side connected with the earth, andthe operation being continued, the maximum of difference willbeat length attained, and the glass is charged. Now if the tw*coatings be connected by a conducting substance the fluid will by-means of its elasticity pass from the positive side to the negative,since there is nothing on either side, or in the discharger, to pre-vent the equilibrium from taking place. It is evident from theabove principles and propositions that the maximum of difference,or greatest charge, will depend on the goodness of the electric plate,on its thickness, and on the intensity of the electrified body byw hich it is charged ; thus, 1. If a worse electric plate be used, othoVthings being the same, the charge will be less, for the particleswhich receive the fluid w ill not retain so great a quantity beforethey communicate a portion to the next in order. 2. If the thicknessof the electric plate be increased other things remaining the samethe charge will be less, for the fluid on the side which receives itwill not so much displace the atmospheres of fluid on the otherside according to what was explained in Prop. I. 3. If the inten-sity of the electrified conductor be less, other things being thesame, the charge will be less, for the intensity of ihe side of theplate which receives the fluid will sooner equal it, and therefore(lie fluid on the other side will be less affected, and hence thecharge will be less. These consequences of the above principle*are found to agree with plixnomena. And here we may observethat an insulated plate is in the case of a very thick electric, andtherefore will not receive a charge.

Prop. IX. If the conductor, to which the coated plate as in thelast proposition is presented, he negative, the plate will receive acharge. For a portion of fluid being taken away from the sidepresented, the pressure is taken from the next particles, and thefluid will lie towards that deficient side: now since the at-mospheres of the particles at the coating connected with the earthare removed from that coating to ihe other side of Ihe parficles,these particles will receive an additional quantity from the earth,and the operation being continued, a maximum of difference willlake place, and the glass will be charged. Note, a little reflectionwill shew that the whole quantity of fluid on the glass is less thanin the case last mentioned, since this is by an abstraction, and thatby a redundancy of fluid.

1’rop. X W bile an electric, plate is charging positively, bothsides will be in a positive state; but after it is" charged, the sidew hich is presented is positive, and the other negative. For theside which is presented receives the fluid at one part, and tiiis fluidbeing dispersed over the coated surface, it will from it; redundancyof fluid begin and continue to discharge it to the surrounding air,and is therefore positive. Also the "other side by the pressme ofthe fluid on it, as above explained, parts witli some of its natural

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