20G USE OF GREEN VITRIOL 



to wave any attention to the hiftory of Mr. Walker's experi- 

 ments, upon which I have animadverted, and to deny his 

 facls. What may have deceived him in his proceedings, his 

 admeafurements, and his repeated regifterings, is not for me 

 to difcufs. If he will fend his lenfes to you, and you fhould 

 find that, under any circumftances whatever of diftance or 

 pofition, it be poffible, by a mere alteration in the aperture, 

 to produce a difference, as 2 to 3, in the length of the focal 

 image, (fee Philof. Journal, Vol. IX. p. 165.) I think it will 

 be incumbent upon us to re-examine all the facts and demonftra- 

 tions, of what we have hitherto been in the habit of calling 

 the feience of optics, in order to reconcile them with fo iirange 

 a remit. 



I am, Sir, 



Your obliged 



C. L. 



XI. 



A Communication on the life of Green Vitriol, or Sulphate of 

 Iron, as a Manure',' and on the Efficacy of paring and burn' 

 ing depending, partly, on Oxide of Iron. By George 

 Pearson, M. D. Honorary Member of the Board of Agri- 

 culture, F. R S. From a Communication made by hi?n to the 

 Board, and inferted in the fourth Volume of their Tranfaclions. 



Sulphate of iron J[ TAKE leave to lay before this Honourable Board, an ac- 

 or martial vitriol r r , n , • . T £ j 



hitherto fuppofed C0l,nt °' a hibltance as a manure, which 1 find, on exarmna- 

 deftru£tive of tion, is one of the things, hitherto univerfally believed to be 

 vegetation, a p jf on to vegetables. Having afcertained that this fubftance 



is what is commonly known by the name of vitriol of iron (the 

 fulphate of iron of the chemifts), inveterate opinion prevented 

 me for fome time from accepting the teftimony of it as a ma- 

 nure; but feeling the weight of the refpectable evidence by 

 whom it was attefted, after confideration I perceived that the 

 fattin queftion was not at variance with eftablifhed principles 

 of vegetable philofophy, as I (hall, I think, make appear in 

 this communication, 

 —but the con- M y friend John Williams Willaume, Efq. of Tingrith in 

 traryistiue. jjedfordftiire, having defired his brother, Charles Dymoke 

 Willaume, Efq. to aik my opinion of a faline fubftance coi- 

 ned 



