C 12 3 



ed with fertility and on this subject many of the for- 

 mer difficulties of investigation will be found to be re- 

 moved by recent enquiries. 



The necessity of water to vegetation, and the lux- 

 uriancy of the growth of plants connected with the pre- 

 sence of moisture in the southern countries of the old 

 continent, led to the opinion so prevalent in the early 

 schools of philosophy, that water was the great pro- 

 ductive element, the substance from which all things 

 were capable of being composed, and into which 

 they were finally resolved. The " -e * "" of 

 the poet, " water is the noblest, 5 ' seems to have 

 been an expression of this opinion, adopted by the 

 Greeks from the Egyptians, taught by Thales, and 

 revived by the alchemists in late times. Van Hel- 

 mont in 1610, conceived that he had proved by a de- 

 cisive experiment, that all the products of vegetables 

 were capable of being generated from water. His 

 results were shewn to be fallacious by Woodward in 

 1691 ; but the true use of water in vegetation was 

 unknown till 1785 ; when Mr. Cavendish made the 

 grand discovery, that it was composed of two elastic 

 fluids or gases, inflammable gas or hydrogene, and 

 vital gas or oxygene. 



Air, like water, was regarded as a pure element 

 by most of the ancient philosophers : a few of the 

 chemical enquirers in the sixteenth and seventeeth 

 centuries, formed some happy conjectures respecting 

 its real nature. Sir Kenelm Digby in 1 660, supposed 

 that it contained some saline matter, which was an 

 essential food of plants. Boyle, Hooke, and Mayow, 



