i 



of E^psrimental Phi'ofophy', 355 



GUr end is obtained, and, for the mod part, 

 we reft fatisfied. But if the proofs fail, fonne 

 unexpecfled phsenomena often occur, which 

 awaken our attention, fuggeft new analogies, 

 and excite us, perhaps, to the inveftigation of 

 other propofitions of more importance than the 

 antecedent ones. The very interefling and 

 comprehenfive difcoveries of Dr. Black, con- 

 cerning the nature of calcareous earths, and 

 alkaline falts, in their different ftates of mild- 

 nefs and caufticity, originated from an incident 

 of this kind. * And many fimilar examples 

 might be adduced from the records of philofophy. 

 But whether fuch be the fortunate event or not, 

 A negative truth may be of as much value as a 

 pofuive one ; and confequently, fuccefs or difap- 

 pointment may prove equally ufefui in experi- 

 mental refearches. j 



To deduce the general charaders of a body 

 from one fingle property of it, individually con- 

 fldered, feems contrary to the rules of philofo- 

 phizing. And the young experimenter Ihould 

 be cautious both of admitting, and of forming 

 fuch analogies. Yet they are fometimes fo ftrong 

 as to force convidlion even againft the evidence 

 offenfe, and of general opinion. The diamond 



• See Efiays Phyfical and Literary. 



f See the Author's E/Tays Medical and Experimental, 

 vol. I. p. 106. edit, third. 



Vol. II. A a was 



