ON POLYGONAL NUMBERS. 33 



air, the juice of acid apples becomes very sweet, and ac- 

 quires many degrees of increased specific gravity; and a si- 

 milar absorption of air, with corresponding effects, is well andinmalting. 

 known to take place in the process of malting. 



I shall conclude with observing, that in retracting the Subsequent 



B . ^ r motion of 



opinion 1 formerly entertained respecting the ascent ot the the sap 



sap in the alburnous tubes, I do not mean to retract any through the 



... iT1 ..„ . . central vessels. 



opinion that 1 have given in former communications re- leaves &batk;. 



specting the subsequent motion of the sap through the cen- 

 tral vessels, the leaves, and bark ; or the subsequent junction 

 of the descending with the ascending current in the albur- 

 num: every experiment that I have made has, on the con- 

 trary, tended to confirm my former conclusions. 



I am, 



My dear Sir, 

 Your much obliged obedient servant, 



THOMAS ANDREW KNIGHT. 



Elton, June 15, 1808. 



VI. 



Letter on Polygonal Numbers, in Reply to Mr. Gough: by 

 P. Barlow, Esq. 



To the Editor of the Philosophical Journal. 

 SIR, 



.R. Gough is perfectly correct in stating, that I was in Re j to Mr< 

 possession of his reply previous to the date of my letter Gough. 

 inserted in your Journal. The reason I did not think pro- 

 per to publish it was, that it was written in answer to a pri- 

 vate letter, which was not exactly the same in form as that 

 published in your number for October, and consequently an 

 answer to the former could not with propriety have been 

 given as a reply to the latter. 



I must now beg leave to be permitted to make a few re- 

 marks on the answers of Mr. Gough inserted in your last 



Vol. XXII. — Jan. I8O9. D number; 





