108 Queries as io Grindstones and Ironstonein Durham, &c. 



vial to one of the cups, a luminous arch was seen filling the top 

 of the s\'phon, and a spark could be drawn from the other cup, 

 thus showing that it was not a conductor of the electric fluid. 



45. There remained to be performed the second part of the 

 experiment and the most difficult, namely, to have the mercury 

 loil in that long syphon. I succeeded in this operation; and when 

 the syphon was placed with its legs in the cups, that complete 

 vacuum ceased to be a conductor. The rain sparks were given to 

 one cup, none was drawn from the other. 



46. This experiment convinced Dr. Franklin of my system, 

 that the electric fluid was a sort oi parasite substance, which, on 

 our globe and its atmosphere, was distributed on all other mat- 

 ters, and nowhere accumulated so as to produce ligktnings, and 

 their common attendants thunders ; but that these phaenomena 

 proceed from the decomposition of the atmospheric air by a 

 certain process, which manifests that the electric fluid enters into 

 the composition of that air, a fluid sui ge?ieris, and not a mix- 

 ture of different kinds of air, as it was supposed in the new che- 

 mical theory. Which conclusion of my long course of experi- 

 ments serves as the basis of my work under the title of Introduc- 

 iio?i a la Physique terrestre par les Fluides expunslbles. 



XIX. Queries, as to Grindstones and Irovsto?ie in Durhamy 

 and Shells, &c. near Cambridge. 



To Mr. Tilloch. 



Sir, — JTIaving read in a cotemporary journal, that Nathaniel 

 Wvnch, Esq. has presented to the Geological Society an account 

 of the Geology of Durham and Northumberland, and has men- 

 tioned therein, that the " grind-stone sill" furnishes the cele- 

 brated Newcastle Grindstones (dug on Gateshead Fell, as I am 

 informed) : now on reference to Mr. VVcstgarth Forsters " Trea- 

 tise on a Section of the Strata," pages 1 19 and 31,1 find him 

 describing the Grindstone sill as nearly the uppermost on Cross- 

 fell mountain, and as sue!), much lower in his Section than the 

 Gateshead -fell Rock, 1 should suppose, but on which I beg to 

 receive information through your work, from Mr. Wynch, Mr. 

 Forster, or any other person, who can point out the particular 

 stratum in Mr. Forster's Section, wherein the Gateshead Grind- 

 stone Quarries are situated. 



Mr. Wynch has likewise mentioned, that " bivalve shells" 

 occur in the clay Ironstone Balls lodged in onp or more beds 

 of shale or slatv clay: and I shall also be obliged by information, 

 &i above, whether the j^hells mentioned resemfjle fresh-water or 



Pond 



