jljg. ^Umaie of Irehxd. — Ek&rtctty 



porary in duration, fo impotent in flrength, afl;ing through the lengthened period and per* 

 fevering efforts of a large portion of his fpecies, can reafonably be deemed equal to the in-' 

 voluntary produdtlon of fuch vaft effefts ; to a change even of the elements and climates 

 of the earth, may admit of doubt, of oppofition, and even of denial. For thefe reafons I 

 have taken the liberty fimply to pvopofe them as matters of enquiry j and only beg the in- 

 dulgence of the Academy for troubling them with matters that may not be- attended witl^ 

 TufEcient evidence to bring convidion, or even to efcape ccnfurc. 



POSTSCRIPT. 



THE prefent year (1795) has been comparatively cold in its commencement, and warm in 

 its fummer : it has been calm, dry, and in many refpeds a contrail to the long ferics of pre- 

 ceding years, whofe effeQs are regiftered in this Mem.oir. 



Yet the extremes of its temperature have not been equal to thofe of former years, as fas 

 *s can be inferred from the recorded effecls of heat and cold on natural objects. Tho 

 large rivers of the northern province have not been bound firmly in the icy chains oS 

 winter, nor have the grapes ripened in favourable afpe^ls in any part ef the kitigdom dur- 

 ing fummer, as formerly occurred in feafons whofe temperature was denominated extreme. 



III. 



Experiments and ObferiKitions on ElecJricity- — Excitation — the two States — Points of Biffereneg 

 between the A8ion of -weak andflrong EleEiricities compared together. ( W. N.) 



Ti 



H E excitation of ele£trics by friQion Hill remains a myftery. We poffefs nothing 

 in the lead refembling a theory of the changes of eledlrical capacity which the rubber and 

 cylinder undergo during their charge of relative pofition in contact. In the year 1789 I 

 communicated Icveral fafls to the Royal Society* concerning the mutual a£lion cf the fillc 

 flap and the ele£lrical cylinder upon each other, and flievved that fomething like eompen- 

 fation takes place while they renjain together. The tranfition of the fu,rface of the cylin- 

 der from the compenfated to the uncompenfated ftate is ftrikingly feen when a hole is cut 

 in the filk, and the cylinder turned under circumftances of confiderablc excitation. A caf- 

 cade of fire iffucs from that edge of the hole which is neaieft the culhion ; but inftead of 

 being diffipated into the air, it bends down again, and unites with the cylinder at the oppo- 

 fite edge of the hole, whence it proceeds as ufual to the repi^iiving part of the prime con- 

 dudor. ' • 



The phenomena of the two eledricitles called plus and minus are fingularly diftinft in 

 almoft every experiment which can be made with the exhibition of eledric light. Paper is 

 a good fubftance for obferving the vifible paffage of eledricity. If a ftrong plus eleftric 

 ftrcam be let fall on the flat fide of an uninfulated (heet of pappr, it forms a beautiful ftar 

 about four inches in diameter, confilting of very diftinft radii not ramified. The minus 

 ♦Icdticlty, in circumftances perfedly fimilar, throws many pointed brufhes to the paper, 



* Plulofophical Tranfa6tions, No. Jixxix. 



bat 



