THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



APRIL 1853. 



XXXVII. On Cavities in Amber containing Gases and Fluids. 

 By Sir David Brewster, K.H,, D.C.L., F.R.S., V.P.R.S. 



Edinb.j and Associate of the Institute of France^. 



HAVING recently had occasion to examine a great number 

 of Diamonds, and having discovered in by far the greater 

 number of them cavities of different shapes, round which the 

 substance of the diamond had been compressed when in a soft 

 state by the expansion of their gaseous contents, I was anxious 

 to re-examine some specimens of Amber in which 1 had observed 

 the same phsenomena, and other specimens which were likely to 

 exhibit them. 



The general character of the cavities in diamond was that of 

 extreme irregularity, and hence the sectors of polarized light and 

 the black cross which separated them partook of the same cha- 

 racter. In most of the cavities in amber, on the contrary, their 

 form was accurately spherical, and the polarizing structure which 

 surrounded them extremely perfect and beautiful. I have found, 

 however, numerous microscopic cavities which are very irregular, 

 and which, like those of the same minuteness in the diamond, 

 give regular sectors of polarized light. I have found also cavi- 

 ties of this kind existing in groups twelve or fifteen in number. 



In a specimen of amber containing spherical cavities of various 

 magnitudes, and exhibiting around them the polarizing structure, 

 I have observed several cavities quite close to them without the 

 slightest trace of such a structure. The circumference of the 

 latter was encrusted with a sort of reddish powder, which had 

 probably been deposited by a fluid that had been carried off by 

 absorption. 



* Communicated by the Author. 



Phil. Mag. S. 4. Vol. 5. No. 32. April 1853. R 



