[ 'J' ] 



inexplicable ; difcoverles of great importance have been made 

 hj Mr. Senebier and Dr. Ingenhouz ; even Mr. Young has 

 not always confined his attention to the mere pradical part, 

 but fometimes happily extended it to objeds of a more general 

 and fpeculative nature ; but the fulled light, perhaps, has 

 been throv^m on this fubje6l by the late difcoverles of Mr. 

 Haflenfraz *. 



If the exacl connedlion of efFeds, with their caufes, has not 

 been fo fully and fo extenfively traced in this as in other fub- 

 jedls, we mufl attribute it to the peculiar difficulties of the 

 inveftigation ; in other fubjeds expofed to the joint operation 

 of many caufes, the effedl of each, fingly and exclufively taken, 

 may be particularly examined ; the experimentor may work 

 in his laboratory with the objedt always in his view ; but the 

 fecret procefles of vegetation take place in the dark, expofed 

 to the various and indeterminable influences of the atmofphere, 

 and require at leaft half a year for their completion ; hence the 

 difficulty of determining on what peculiar circumflance fuccefs 

 or failure depends ; the diverfified experience of many years 

 can alone affiard a rational foundation for folid fpecific con- 

 clufions. It cannot therefore be expedled that new^, decifive 

 and diredl experiments fhould be laid before the Academy 

 within the time prefcribed for anfwering this queflion. The 

 refolution. of the firfl part mufl be deduced from a flatement 



R 2 of 



* Annales Chymigucs, Vol. 13. 14. 



