§ 28. THE DIAMOND. 705 



charcoal. Sir Isaac Newton remarked, that the refractive 

 power, that is, the property of bending the rays of light, 

 was three times greater in respect of their densities, in 

 amber and in the diamond, than in other bodies ; and he 

 therefore concluded that the diamond was some unctuous 

 substance that had crystallized. 



Sir David Brewster observed, that the globules of air 

 (or some fluid of low refractive power) occasionally seen in 

 diamonds, have communicated, by expansion, a polarizing 

 structure to the parts in immediate contact with the air- 

 bubble, a phenomenon which also occurs in amber. This 

 is displayed in four sectors of polarized light encircling the 

 globule of air ; a similar structure can be produced arti- 

 ficially, either in glass or gelatinous masses, by a compres- 

 sing force propagated circularly from a point. This cannot 

 have been the result of crystallization, but must have arisen 

 from the expansion exerted by the included air on the 

 amber and the diamond, when they were in so soft a state 

 as to be susceptible of compression from a very small force; 

 hence Sir David Brewster concludes that, like amber, the 

 diamond has originated from the consolidation of vegetable 

 matter, which has gradually acquired a crystalline form by 

 the slow action of corpuscular forces.* 



Liebig concurs in the opinion that the diamond is of 

 vegetable origin, and offers the following remarks on its 

 probable mode of formation. 



" If we suppose decay to proceed in a liquid containing 

 carbon and hydrogen, then a compound with still more 

 carbon must result, in a manner similar to the production 

 of the crystalline colourless naphthalin from a gaseous 

 compound of carbon and hydrogen. And if the compound 

 thus formed were itself to undergo further decay, the final 

 result must be the separation of carbon in a crystalline 

 form. Science can point to no process capable of account- 

 ing for the origin and formation of diamonds, except that 

 * Geolog. Trans, vol. iii. p. 459. 



