LEVELS OF FRANCS. ^I'J. 



any fluoric acid been prefent. Finding this, therefore, to be ndcher wa> 

 (he cafe, I proceeded as follows: — Fifty grains of the ^^me ^'^^^'^^^J].-^'^^^^'"^ 

 enamel were introduced into a fmall glafs retort, and a little acid by adoir.s 

 fulphuric acid being added, dittillation was carried on "^^''b' en'!m»Und dif- 

 to drynefs, but in tuch a manner, that the gafeous produds tilling over mej* 

 might be received over mercury. A fmall quantity of fulphuric '^^^'^' 

 acid gas was difengaged, and what remained in the retort, 

 confided, as far as I could afcertain, of a mixture of fulphate 

 of lime, phofphoric acid, and a fmall portion of fulphur, 

 arifing from a decompofition of a fmall part of the fulphuric 

 acid by the animal matter, exifting in the enamel. 

 I have the honour to be. 

 Sir, 



Your moft obedient fervanf, 



WILLIAM ERANDE. 

 Arlington Street, 

 Feb. 15, 180G. 



VIIL 



A Memoir on taking the Levels of the whole Surface of France. 

 By P. S. GiUARD, Chief Engineer of Bridges and High- 

 ways, S^c* 



IF the furface of the earth were formed by the revolution of 

 a curve round its axis, it would be fufficient, in order to de- 

 termine the refpedive pofilions of different points upon it, to 

 meafure their diftances from the interfedion of that furface 

 made by the plane of the equator and any particular or af- 

 furaed meridian. 



Thus geographers, confidering the earth as perfe6ily fphe- The method by 

 rical, have determined the pofition of any given place by the ^^j|^"'^^'^^S""_ 

 Conjun6lion of two co-ordinates, one of which is the arc of the pofuioji 9j^ » 

 the meridian, comprlfed between the place and the equator, P'^<^^» 

 and the other an arc of the circle parallel to the equator, com- 

 prlfed between the place and any afligned meridian, 



* Journal des Mines, Vol. XVII. p. 257. 



As 



