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1 
SIR, Paris, Aug. 21, 1752. 
Read Nov. 23, A Phenomenon, which I have always 
j C jL thought worthy of ftriCt obferva- 
tion, is the diminution of the ele&ricity of thunder, 
when rain comes on during the ftorm. This dimi- 
nution was remarked at St. Germain, every time I was 
a witnefs to M. le Monnier’s experiments j and the 
fame efFeCt is, within this little while, confirm’d to 
me by the learned Mr. Euler, in communicating to 
me the obfervations of M. Ludolf. I have thought 
of only three caufes aflignable to this phenomenon, 
which I lay down in the following order : 
1. Does not this diminution happen, becaufe the 
drops of water, that run down the little bar of iron, 
carry with them the electricity of the bar ? 
2. Does not the rain, in pafiing thro’ the atmo- 
fphere, deprive or {trip it of the electricity, which 
is communicated to it by the thunder ? 
3. Or elfe, is it not more likely, that the diminu- 
tion, and the total ceflation, of the eleCtrical itreams 
happen then, either becaufe the matter of the thun- 
der is exhaufted, or becaufe the clouds coming to 
difi'olve, the eledtrical matter is loft and difiipated ? 
5, I left St. Germain the 12 of July to come to Paris, 
at 7 in the evening. At the inftant of my arrival, I 
faw the heavens cover’d with >clouds, and the light- 
ning foreboded thunder, which was foon heard. I 
went up into the gallery of the Hotel de Noailles, 
which is very high, and diftant from the neighbour- 
ing buildings: my pole was 10 feet high; at the 
end of which a glafs tube was made fail; ; and to this 
a very {harp iron fpire, from the middle of which a 
Zz z 2 wire 
