HEAD OF FLINT. 



195 



with the idea of rarefaction attached to such lightness. It is 

 evidently owi::g therefore to the multitude of pores and hol- 

 low spaces, into which the water cannot penetrate, to cir- 

 cumscribe the volume of the solid parts. Powdered pumice Its 5 P e c grav. 

 stone afforded me a specific gravity of &*142*; and this is p orou ' s sub _ 

 the only method of weighing hydrostatically porous bodies, stances should 

 so as to obtain a constant expression of their density, truly powc ier. 

 comparable, and affording a just idea of the power of ag- 

 gregation possessed by their integrant parts, which is the most 

 important point, on which any light can be thrown by a com- 

 parison of specific gravities. 



X. 



Report on a Sculptured Head of Flint, ivith a Covering of 

 Calcedony, made to the Physical and Mathematical Class 

 of the Institute, March 31, 1806. By Mr. Guy ton f. 



.R. MILLIN, our associate, of the class of history and Antiqtie sub- 

 ancient literature, having had an opportunity of examining mitted to the 

 a piece of sculpture found in the Faubourg du Roule, l ™jSjf?-^* 

 thought it his duty to offer it to the inspection of the phy- 

 sical and mathematical class, as an object leading to ques- 

 tions that were interesting both to mineralogy and the arts ; 

 and yon have commissioned Messrs. Berthollet, Vauquelin, Committee. 

 and myself, to make a report to you on the subject. 



The fragment was very obligingly entrusted to us by Mr. 

 Cerf, to whom it belongs. It was found, four months ago, Where f oun a. 

 in the garden of a house, that was formerly part of the 



* See Annates de Chimie, Vol. XXIV p. 204 



N. B. 1 did not neglect this method of verifying the specific gravity 

 of the filtering stone. I reduced it to a fine powder ; and the moment it 

 was immersed in water, all the air interposed between its parts, or rather 

 that adhered to its surface, rose in one single bubble; and the loss of 

 weight indicated, without any correction, a specific gravity of 2-261, 

 which differs very little from that I mentioned before. 



f Annates de Chimie, Vol. J/VIII. p. 75. 



Chateau 



