C 437 ] 
In repeating fuch of the experiments with the 
’Tourmalin as were moft proper to anfwer your ob- 
jections, I accidentally obferved an appearance which 
has given rife to-fome new experiments, very fimple, 
and of great confequence in eleCtric refearches. 
Thefe dilcoveries you fhall be acquainted with, 
before I conclude this letter, that I may have the 
pleafure of hearing your fentiments concerning them, 
the fooner. 
I am glad to find we * agree in admitting what are 
called the two fpecies of eleCiricity, one whereof con- 
fifts in the augmentation of the eledtric fluid, and the 
other in it s diminution. But ftill, notwithftanding the 
experiment made with the bent tube in order to deter- 
mine that interefting queftion, you feem to doubt which 
of thefe is the plus , and which the minus electricity. 
1 ou fay •'j'* 1 have proved the oppofition of the two 
fpecies, by the knobs of light appearing at the up- 
per 
* Mi . Wilfon reconnoit de meme que moi, l’exiftence de deux 
cfpeces d eledtricite, dont l’une confifte dans ^augmentation, et 
1 autre dans la diminution, de la quantite naturelle du fluide elect- 
nque. ^ C eft une queftion qui doit interefler chaque phyficien, 
de demeler, quelle de deux eleCtricites, ou la vitree, ou la refineufe 
de Mr. du Fay, eft la pofi-ive, et quelle en eft la negative ? 
Cguant a moi j’ai declare, il y a long terns, dans raon Sermo de 
Jimilitudine electriatatis et magnetifmi , que je ne connois aucune 
experience, propre a decider cette queftion. Je fuis maintenant 
encoie du meme fentiment, car la belle experience de mylord 
Charles Cavendifti, rapportee ici et perfecHonee par Mr. Wilfon, 
me femble laifler pareillement la chofe indecife. 
. + Quant a l’oppofttion des deux efpeces d’elearicite, je con- 
viens qu’elle eft fort clairement prouvee par l’experience de Mr. 
Wilfon, et par ce phenomene, que la lumiere elearique eft beu- 
coup plus vive qu’ailleurs dans le vuide, aux furfaces fuperieures 
es colomnes du mercure, (jufqu’a y former commedes boutons 
Vol.LIII. L 11 
