TOL. XLTII.^ PHILOSOPHICAL TIAN8ACTIONS. '1^3 



Towanls 1 1 in the morning, the heavens began to be covered to the south- 

 west, with stMne claps of thunder and lightning at a gR^at distance. The AbW 

 had just time to go to the garden, where he found tiie Duke d'Ayen, wlio had 

 p(e|Mured ever)- thing for the experiments. An iron wire descended from the top 

 of tlte pole, and rested on the hot-house of the garden : this wire was supportetl 

 by m silken cord, and was tenninatetl by a tin cylinder, of about 3 inches dia- 

 meter, ami 3 feet long. The electricity of this cylinder was such that, when a 

 finger approached it, 'i or 3 very lively sparks at a time were proilucetl, with a 

 iliarkling noise, like that of the nails of one's fingers crackled against each other. 

 Tlien the Duke d'Ayen took the first shrub he met in the hot-house, which 

 happened to be that from which the labdanum is producetl : he placed it with its 

 pot on a cake of resin, and fastened the iron wire to one of its branches. This 

 shrub was instantly electrized, so tliat whitisli sparks issued from every leaf, witli 

 the same kind of crackling just mentioned ; but the trunk of this shrub had a 

 much stronger electricity ; whether at that instant the electricity of the cloud 

 was more stanig, (for it \-aries every moment) or that the force of the whole 

 electricity, expamled through the leaves, became concentrated in the trunk of 

 this shnib. 



Tlie duke then took one of his silver watering-pots, which was 24 feet high ; 

 he rilled it with water within an inch of the brim, and placed it on the 

 electrical calie, dipping into it a wire of lead, which communicated with that 

 wire which came from the top of the pole. Of all the electricity tried till then, 

 this was incomparably the strongest; there were 20 sparks; and on advancing the 

 ringer towards it, the shock affected the arms and breast with great violence. 



Letters. Dated Paris, August 1\, 1732. — A phenomenon, which I have 

 always thought worthy of strict obser\'ation, is the diminution of the electricity 

 of tliunder, when rain comes on during the storm. This diminution was re- 

 market! at St. Germain, every time I was a witness to M. le Monnier's experi- 

 ments ; and the same effect is, within this little while, confirmed to me by the 

 learned Mr. Euler, in communicating to me the observations of M. Ludolf. 



I left St. Germain the 12th of July to come to Paris, at 7 in the evening. At 

 the instant of my arrival, I saw the heavens covered with clouds, and the light- 

 ning foreboded thunder, which soon was heard. I went up into the gallery of 

 the Hotel de Noailles, which is very high, and distant from the neighbouring 

 buildings : my pole was 10 feet high ; at the end of which a glass tube was made 

 fest ; and to this a very sharp iron spire, from the middle of which a wire of 

 about 20 /eet long came down, and rested on a long glass tube fixed to the ba- 

 lustrade, which environed the galler}-. My apparatus was scarcely ready, when 

 it thundered, and the clouds broke by this first clap, and poured down a conti- 



