STEPHEN HALES 135 



and the hydrogen disappears by combining with 

 the oxygen set free. This was expressed in the 

 language of the day as the reconstruction of metallic 

 lead by the addition of phlogiston (the hydrogen) 

 to the calx of lead (minium). Thorpe points out 

 the magnitude of the discovery that Priestley 

 missed, and it may be said that Hales too was on 

 the track, and had he known as much as Priestley 

 it would not have been phlogiston that kept him 

 from becoming a Cavendish or Lavoisier. What 

 chiefly concerns us, however, is the bearing of Hales' 

 chemical work on his theories of nutrition. He 

 concludes that "air makes a very considerable part 

 of the substance of Vegetables," and goes on to say 

 (p. 211) that "many of these particles of air" are 

 " in a fixt state, strongly adhering to and wrought 

 into the substance of" plants.^ He has some idea 

 of the instability of complex substances, and of the 

 importance of the fact, for he says^ that "if all the 

 parts of matter were only endued with a strongly 

 attracting power, [the] whole [of] nature would 

 then become one unactive cohering lump." This 

 may remind us of Herbert Spencer's words : "Thus 

 the essential characteristic of living organic matter, 

 is that it unites this large quantity of contained 

 motion with a degree of cohesion that permits 

 temporary fixity of arrangement " {First Principles, 

 § 103). With regard to the way in which plants 

 absorb and fix the "air" which he finds in their 



' He speaks here merely of the apples used in a certain experi- 

 ment, but it is clear that he applies the conclusion to other plants. 



' Vegetable Staticks, p. 313. It should be noted that Hales 

 speaks of organic as well as inorganic substances. 



