ON THE PHYTOLACCA. 85 



piston is given, multiply the length of the scale by the 

 squai-e of the internal dian«i|^r of the le<^ B C, and divide 

 the product by the square ojf the given diameter, and the 

 quotient will be the length of the piston : 2d. When the 

 length is given, divide the product found above, by the given 

 length, and the square root of the quotient will be the dia- 

 meter of the piston, hi adjusting these dimensions, we 

 have two circumstances of some importance to attend to ; 

 the quantity of mercury requisite to charge the tube in- 

 creases with the length of the piston, winch suggests a con- 

 sideration of an economical nature; but if the diameter of 

 the piston be too much augmented, to avoid expense, the 

 free motion of the barometer will be considerably impaired; 

 the artist must therefore use his own judgment in giving 

 those dimensions to the piston, which will be the most conve- 

 nient for the tube he is going to fit up. 



I remain, Sec, 



JOHN GOUGH. . 



II. 



Ohsefvattons on the Phytolacca^ or American Poke?veed; hy 

 Mr. H. Braconnot, Member of the Academy of Sciences^ 

 Sfc. at Nancy*, 



AN, who lays all nature under contribution, to increase T^e properties 

 his enjoyments, has availed himself of a i^reat number- of ° if ^"^.^"k^** 



'J " r3 iciTldlu CO 06 



vegetable productions; but, notwithstanding his extensive examiutd. 

 researches, he is yet far from being acquainted with the p'o- 

 perties that characterise the majority of plants. The Phy- 

 tolacca, which has been greatly neglected, may furnish an 

 instance of this. 



Sect. I. 

 Tnchieralion of the phyfolacca. 



THIS plant, which is acrid, has a very thick, fleshy root, Phytolacca. 

 ^s big as a man's leg. Its stalks are as big as a large waik- 

 iiig stick, six or seven feet high, and purple. 



•Abridged from the Annales de Chinile, Vol. LXXII, p. 71, April 1807. 



If 



