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LETTER XV. 



AMBER. ...KNOWN TO THE EARLIEST WRITERS IN NATURAL HIS- 

 TORY.... JET....SUCCINUM NIGRUM OF THE ANC IENTS....CA NNE L 

 COAL.... DIFFERENCE. BETWEEN IT AND JET. 



ASSUMING that the substance treated of in this letter, is a bitu- 

 minous substance, deriving its origin from the operations of a pe- 

 culiar process on vegetable matters, which have been long buried 

 in the earth, I shall introduce its history here, among those of the 

 purer bitumens ; reserving the examination of the various opinions 

 respecting its nature and origin, until I have endeavoured to point 

 out the general principles on which, I presume, changes of this na- 

 ture depend. 



Amber, the electrum of the ancients, is a bituminous, inflammable 

 substance, of a yellow colour ; varying in its shades of colour, as 

 well as in its degree of transparency. Its fracture is conchoidal, 

 and manifests a glassy lustre ; and it is susceptible of a fine polish. 

 Its specific gravity is 1.078 to 1.085. By friction it yields a pecu- 

 liar odour, and acquires the property, in a high degree, of attract- 

 ing to it light substances. 



Amber appears to have been known to the earliest writers in na- 

 tural history. Thales of Miletus was highly interested by its elec- 

 tric property. Herodotus mentions the places where amber had 

 been found ; and its peculiar qualities were well known to Aristotle 

 and to Plato. Philemon classed it among fossils, and distinguished 

 it into two kinds, the white and the yellow ; which, he relates, were 

 taken out of two different mines in Scythia. Pliny*, who fre- 



* Lib. xxxvii. cap. 3. 



