po Greek Firt.'—Extra^ioft and Purijication of Oil, 



•circle. M. Venturl informs us, that from a drawing in the manufcrip,t it does not appeat 

 to have been different from the inftrument now in ufe. 2. An inftrument to fliew the 

 conftitution and denfity of the air, and when the weather inclines to rain. From the 

 figure it appears to have been a balance loaded at each end, and provided with a graduated 

 circle to fhew its changes of inclination. M. Venturi thinks that one of the weights iri 

 equilibrio was a body proper to become charged with the humidity of the atmofpherc. 

 This does not very well agree with the confideration of denfity, though it muft be con- 

 feffed that the equal magnitudes of the two weights in the drawing do not give much 

 countenance to the notion of its having been a ftatical barofcope. 3. A leathern cafe or 

 clothing for a diver in the pearl lilhcry. 4. A piece (baton ) which locks alternately in the 

 teeth of a crown wheel to operate like the verge of the balance in clocks ; but for what 

 purpofe is not faid *. 



XIV. Two chemical procfefles. — i. A flaming ball compofed in the following manner :— 

 Take the charcoal of willow, nitre, brandy, refm, fulphur, pitch, and camphor. Mix the 

 whole together over the fire. Plunge a woollen cord in the mixture, and form it into balls, 

 which may afterwards be provided with fpikes. Thefe balls being fet on fire, are thrown 

 into the enemy's vefiels. It is called the Greek fire, and is a fingular compofition, for it 

 burns even upon the water. Callinicus the architeft taught this compofition to the Ro- 

 mans (of Conftantinople), who derived great advantage from it, particularly under the em- 

 peror Leo, when the Orientals attacked Conftantinople. A great numbed of their veflels 

 were burned by means of this compofition. 



2. Oil fit for painting. Choofe the moft perfcv^ nuts, take off the fiiell, foak them in a 

 veflel of water to feparate the (kin ; then leave the kernels in clear water, which is to be 

 changed as often as it becomes turbid, which may be fix or eight times. After a certain 

 time, the nuts on being ftirred will be found to mix with the water, and form a folution 

 refembling milk. Expofe this in plates to the open air, and the oil will rife to the furface. 

 In order to obtain this oil very clean and pure, provide cotton wicks, one end of which is 

 to be dipped in the oil, while the other part pafles over the border of the veflel, and de- - 

 fcends into the neck of a glafs phial two inches below the furface of the liquor in the 

 plate. The oil will by degrees filtrate along the wick, and pafs very fine into the phial, 

 all the impurities remaining in the plate. All the oils of grain and of nuts are equally clear. 

 It is the manner of extradting them which renders them foul. 



The compofition of the Greek fire here given by Vinci, is found nearly in the fame 

 ■words in Baptifta Portaf, whence it appears that both authors derived their information 

 from the fame fource. The modern difcoveries in chemiftry refpe£ling combuftion have 

 dlfclofed the whole fecret of compofitions which burn without accefs to the atmofphere, 

 but by means of oxygene afforded from nitre. The balls defcribed by Frezler J, which 

 fliine on the furface of water, are nothing elfe but the Greek fire. 



XV. Concerning method. — It is always of advantage to the underftanding to acquire 



• The interefting commentary or note on this laft jjaffage has already been given, for the moft part, at 

 page 51 of tht prefent number, 



+ Mag. Natur. lib. xii. cap. i. 



J Des feux d'artifices, edit, de 1747, p. 355. See alfo p. 334, 



knowledge 



