lO A "Reply to Mr. Plajfair's RrfleBhns on 



rows nothing from analog)', it admits of no proof and re- 

 quires no retutation." I was, however, led into ihis opinion 

 by analogy with Mr. Gadd's experiments in the 32d volume 

 of the Memoirs of Stockholm ; for he tells us, that if clay 

 and calces of iron be plentifully mixed with oi', they will 

 form a mafs which will harden even under water. If Mr. 

 Playfair were acquainted with Mr. Chladni's opinion, that 

 thefe malTes were fragments of a broken planet that fell within 

 the fphere of attradlion of our globe, he might pofiibly think 

 . it the mod y/«j-a/t?r ; yet even fo, it is probable he would 

 «ot facrifice the plcafure of beftowing that dillinguiflied epi- 

 thet on mine. However, as he judged my conjefture, I 

 know not on what foundation, inconliltent with the princi- 

 ples of chemical fcicnce, 1 have mixed rult of iron with pe- 

 trol, and afterwards with petrol to which fulphur was added, 

 and found it difpofed to coalefce in a few days. 



P. 422. " One of Mr. Kirwan's objeftions to the depofi- 

 tion of materials at the bottom of the fea is thus ftated : — ■ 

 * Frill has remarked, in his mathematical difcourfes, that if 

 any confiderable mafs of matter were accumulated in the 

 interior of the ocean, the diurnal motion of the globe would 

 be dillurbed, and confequenllv it would be perceptible.* 

 The appeal made here to Friii is (ingularly unfortunate, as 

 that philolbpher demonfi rated the contrary to Mr. Kirwan's 

 pofition. The inllance juft given may ferve as one of many 

 to (how what confidence is to be placed in that undigefted 

 mafs of fai!-ls and quotations which Mr. Kirwan, without 

 difcrimination and without difcuflion, has brought together 

 from all quarters." Mr. Playfair might, however, eafily 

 infer, from the loofe manner in which Frifi is quoted, 

 (namely, in Jome of his mathematical trcatifes, fo different 

 from my ufual manner, in which the pane I take from is 

 mentioned,) that I had not that author before me; and, in 

 fact, I took it from Mitterpacher's Phvfical DcTcription of 

 the Earth, p. 25, who fays, that according to Frifi, in the 

 cafe above mentioned, the velocity with which the centre of 

 the globe would move would be increafed ; omit'.ing the 

 calculation, and the mention that the increafed velocity 

 would not be fe'njible for a long period of years. I hope 

 therefore it is the only one out of the many quotations I 

 have made in which any miftake can be found : if Mr. Play- 

 fair could find any other, he doubtFefs would have mentioned 

 it. The attempt to weaken the force of the numerous fafts 

 I collefted, adverie to the Hutlonian theory, by calling them 

 an und'igcjled mafs, is curious, and, if allowable, would fur- 

 tiilh a very convenient and expeditious method of getting rid 



of 



