ab ipso lente dimittitur), fila iterum discedunt pro excessu ignis aerei supra ignem in catena; qui denique aereus ignis, quoniam lentissime dimittitur, diutissime pergunt divergere fila.

EXPERIMENTUM VIII.

19. Si fila sint nexa machinæ, eadem omnia in iis contingunt phænomena ex diuturna electricitate machinæ, quæ in iis contingebant catena nexis ex diuturna electricitate catenæ.

20. Quare universe, quemadmodum constitui a principio, "Si ignis proprius corporum, quantuscumque is sit, libratur cum igne ambientis aeris, corpora vel consistunt in nativo statu, vel ad ipsum redeunt; si alter ignis superat alterum, corpora discedunt vi ignis superantis."

21. Atque hinc rationem vides, ni fallor, vir præstantissime, cur æque discedant tum quæ a catena, tum quæ a machina sunt electrica corpora. "Ignis proprius in corporibus a catena electricis vincit aereum, aereus vincit æque proprium in electricis a machina."

EXPERIMENTUM IX.

22. Quoties fila mutuo discedunt a se invicem, atque divergunt ex aucto in ipsis, vel minuto igne nativo, ad meum accedunt admotum digitum; quoties discedunt, atque divergunt servantes ignem suum nativum ex aucto, vel minuto igne nativo aeris, a digito refugiunt meo.

23. Hæc vero res primo quidem notissimis legibus accessionum atque discessionum electricarum est consentanea; quum enim nativus in filis ignis auctus est, vel minutus, ipsa sunt inæqualiter ac digitus electrica, qui habet nativum ignem suum; quum vero nativus ignis perstat in filis, et ipsa discedunt mutuo ob ignem auctum, vel minutum in aere, tum, quemadmodum discedunt ambo alterum abs altero, ita discedant oportet a digito meo ipso etiam habente ignem nativum, vi aeris, in quo nativus ignis minutus est, aut auctus. Sed præterea hæc filorum a digito discessio ipsa hanc probat etiam, quam affero, discessionis causam; nam et digitus, et fila, cum solo communicant, adeoque alium in se certe non habent ignem, nisi nativum, quo quoniam non discedunt, restat ipsa discedere ex nativo igne in aere aucto, vel minuto.

24. Cum in hanc primo incidi discessionum electricarum theoriam, ea me ancipitem tenuit suspicio, ne ignis aereus discessiones facere non posset in machina iis æquales in pernicitate, et magnitudine, quas facit in catena ignis proprius; hæc inde subibat

animum suspicio, quod ignis in machina, et catena (universe in corporibus omnibus deferentibus) mensura mutetur quam pernicissime, lentissime autem augeatur, aut minuatur mensura ignis in aere ambiente. Alia præterea suspicionem exaggerabat consideratio; tantum me nunquam abs aere, quantum a machina, subtrahere ignem potuisse, tantum potuisse nunquam aeri addere, quantum catenæ; nunquam enim eo veni, ut omnem aerea sola electricitate sustulerim filorum divergentiam, quanta existebat ex integra machinæ aut catenæ electricitate.

Factum inde est, ut experimenta hæc eadem, imo et alia, in literis attulerim ad præclarissimum instituti Bononiensis præsidem datis, quin hanc in iis satis late theoriam discessionum constitu

erem.

Verum re maturius perpensa intellexi pernicitatem discessionum, quæ fiant abs igne aereo, non ipsi pernicitati respondere debere, qua vel augeatur ipsius copia, vel minuatur; sed pernicitati, qua agat copia inhærens; et magnitudinem discessionum, quæ fiant ab igne eodem, non absolutæ, sed comparativæ ipsius magnitudini respondere debere; utrumque autem facile vidi pro re obvenire.

EXPERIMENTUM X.

25. Si in Experimento VI. post minutam ex diuturniore electricitate catena filorum divergentiam, non lente, sed protinus (manu nempe in catenam immissa) omnem subtraho a catena redundantem ignem, continuo incipiunt quidem accedere fila quam velocissime; verum velocitate æquali resiliunt repente, antequam pertingant ad nativam directionem. Hæc autem altera discessio quoniam fit ex aereo igne superante proprium in filis residuum, video inde ignem aereum (quamquam mutetur lentissime ipsius copia) ipsum tamen discessiones facere iis æque veloces, quæ abs igne proprio efficiuntur.

EXPERIMENTUM XI.

26. Sed et ipsas ex igne aereo obvenire æque magnas ita intelligo. Post ignem inditum in aerem, qui catenam ambit quantus potest, dempto redundante omni ab catena igne, atque adeo discedentibus jam filis ex igne aereo, vitreo globo substituo sulphureum, atque ex hujus functione, video, principio augeri angulum divergentiæ, quem effecerat ignis aereus, tum ipsum continenter minui. 27. Id autem certum; primas globi sulphurei frictiones demere partem nativi ignis a catena, neque pariter demere excessivum ignem ambientis aeris (aer enim lente, ut vidimus, accipit ignem

alienum, lente acceptum exuit); quare augescit magnitudo divergentiæ, quæ fit abs igne aereo, non mutata magnitudine absoluta ignis aerei, sed mutata solum magnitudine ipsius comparativa, minuto nempe igne proprio; adeoque aucta proportione aerei ad proprium. Igitur quoniam quantum ignis ingeritur in catenam, tantundem subtrahitur a machina; proportio ignis aerei circa machinam ad residuum in machina eadem erit ac proportio ignis in catena redundantis ad aereum circa catenam; quamobrem aereus circa machinam discessiones faciet non æque veloces solum, sed et æque magnas, ac eæ sunt, quas facit ignis proprius in catena.

28. Itaque, ut omnia demum paucis complectar, quæ pertinere videntur ad motus electricos universe omnes explicandos (suspensiones enim, adhæsiones, vibrationes, infinitosque alios compositiores quasi ludos electricos, tu ipse probe videre visus es discessionibus omnes, atque accessionibus contineri),hæc denique est summa hypothesis meæ. "Accessiones corporum inæqualiter electricorum efficiuntur ab igne electrico a corpore altero, in quo copiosior est, effluente in alterum per aerem interjectum, ipsumque disjiciente. Discessiones autem vel igne proprio corporum efficiuntur se expandente contra aereum, vel aereo se expandente valentius contra proprium;" quæ tamen expansio ignis alterius alterum superantis sine mixtione mutua alterius cum altero videtur contingere. Aer enim ignem continet suum quantumcunque, ne discedat; arcet proprium deferentium corporum ignem, ne adhærescat sibi.

29. Hanc, inquam, hypothesim offero tibi, vir præclarissime, quo tu eam facias meliorem. Si tanti interea ipsam ducas, ut Regiæ isti scientiarum Societati exhibenda videatur, res ex meo obtinget desiderio, qui quando ornamentum ipsi adferre nullum possum, diligentiam saltem nolim desiderari meam. Tu vero cura, ut valeas. Servari enim te decet quam diutissime utilissime, scientiæ perficiendæ amplificandæque, quam certissimam instituisti.

Dat. Taurini, 24 Decembris, 1757.

Remarks on the preceding Paper, by Dr. Franklin.

For the better understanding this paper, it is necessary to know, that Father Beccaria uses a large chain, suspended by silk lines, for the purpose of a prime conductor; and that his machine for turning the glass globe is so contrived, as that he can, on occasion, readily isolate it (that is, place it on glass or wax), together with the person that works it. When the communication is thus cut off between the earth and the chain, and also between the earth

and the machine, he observes, that, the globe being turned, both the chain and the machine show signs of electricity; and, as these signs, when examined, appear to be different in the chain and in the machine, and the globe having, as he supposes, drawn from the machine part of its natural or common quantity of electricity, and given it to the chain, he calls the electricity appearing in the chain, electricity by excess; and the electricity appearing in the machine, electricity by defect; which answer to our terms of positive and negative electricity, or electricity plus and minus. And thus his expressions, electrifying by the chain, and electrifying by the machine, are to be understood, electrifying positively, and electrifying negatively.

No. V.

LETTER FROM PROFESSOR THORBERN BERGMAN, OF UPSAL, TO BENJAMIN WILSON.*

Remarks on One of Franklin's Experiments in Electricity. READ AT THE ROYAL SOCIETY, NOVEMBER 20TH, 1760.

DOMINUS Franklin in § 28 tertia epistola miratur glaciei frustum non transmittere commotionem electricam, cum aqua idem perfecte præstet; sed feci nonnulla experimenta, quæ monstrant parvam aquæ quantitatem nec huic fini sufficere. Scilicet capiatur. tubus vitreus trium vel quatuor pedum, qualis barometris inservit ; hic aqua impleatur, et claudatur utrumque extremum subere perforato filo metallico aquam paululum intrante, uti figura adposita indicat.

AE

-A

Si jam duo homines in circulo explosorio constituti teneant extrema filorum metallicorum, A, A, et tentetur evacuatio, non tamen perfecta evenit, nam vix carpus et rarissime flexura cubitus hac methodo

* This letter is dated at Upsal, October 17th, 1760. An extract only is here given. The remainder of the letter relates to a different subject. See the whole in the Philosophical Transactions, Vol. LI. p. 907. EDITOR.

See p. 209 of the present volume. — EDITOR. VOL. V.

65

concutitur, licet deinde idem vas absque ulteriori cumulatione tantum contineat electricitatis, ut more consueto evacuatum pectus valide ferire possit. Aucta tubi capacitate, magis transit, usque dum ita increverit, ut plenarium transitum permittat, nec impedit aquæ quantitas justo major, quod testantur commotiones per lacus et flumina propagatæ. Conveniunt itaque aqua et glacies in eo, quod parvæ quantitates concussionem ægre tramittant.

Hinc suspicatus sum magnam glaciei quantitatem faciliorem concedere transitum, quod etiam experientia comprobavit, etsi adhuc non majus adhibui frustum quam quo commotio flexuram cubitus attigit. Præterea ex æqualibus aquæ et glaciei quantitatibus, glacies minus transmittit.

No. VI.

LETTER FROM M. DUBOURG TO M. DE LOR.*

Parallel between the Theories of Franklin and Nollet.

SIR,

I return you the History of Electricity, which you had the goodness to lend me, with my thanks for it. Mr. Priestley's zeal for the glory of Mr. Franklin has given umbrage to the editor, who is animated with a zeal no less ardent for the memory of the Abbé Nollet. Which would all be very well, if he did not attempt to make it a party matter between the French and English. Let us leave these national prejudices to the common people; let political ministers espouse their passions, if they think they can make them subservient to their designs; but let not philosophers be influenced by these petty local considerations. The republic of letters is one; let us have a care that we do not dismember it; it allows distinctions, but abhors a division. Nollet, Franklin, Hawksbee, Muschenbroeck, pinus, Wilson, and Beccaria are all fellow-citizens, and we should regard them all with equal favor.

I will give you candidly, and I would repeat it with the same frankness before all the world, my opinion of Franklin and of

* Translated from M. Dubourg's edition of Franklin's works. M. de Lor was Professor of Experimental Philosophy in Paris. — EDITOR.