844 EPOCHS IN THE HISTORY OF THE CONTEMPLATION OF 



it to the escape of a "celestial fiery substance" causing levity; 

 but it was not until eighty years afterwards, that Jean Rey, an 

 exceedingly skilful experimenter at Bergerac, who had ex- 

 amined with great accuracy the increase of weight during the 

 calcination of lead, tin and antimony, enounced the important 

 'result that the increase of weight was to be attributed to the 

 accession of air to the metallic cak, saying, " Je responds 

 et soustiens glorieusement que ce surcroit de poids vient 

 de Fair qui dans le vase a este espessi." ( 53 ) 



Men had now entered on the path which *was to conduct 

 to the chemistry of our days, and through it to the knowledge 

 of a great cosmical phenomenon, the connection between the 

 oxygen of the atmosphere and the life of plants. But the 

 combination of ideas which next presented itself to distin- 

 guished men was of a singularly complicated nature. Towards 

 the end of the 17th century there arose, obscurely with 

 Hooke in his Micrographia (1665), and more distinctly with 

 Mayow(1669,) and Willis (1671), a belief in the existence 

 of nitro-aerial particles, (spiritus nitro-aereus, pabulum nitro- 

 sum), identical with those which are fixed in saltpetre, 

 contained in the air and constituting the necessary condition 

 of combustion. " It was stated that the extinction of flame 

 in a close space does not take place from the air being over- 

 saturated with vapours proceeding from the burning body, 

 but that this extinction is a consequence of the entire ab- 

 sorption of the nitro-aerial particles ("spiritus nitro-aereus") 

 which the air at first contained." The suddenly increased 

 glott when melting saltpetre (emitting oxygen) is strewed 

 upon the coals, and the exudation of saltpetre on clay walls 

 in contact with the atmosphere, appear to have conduced to 

 this opinion. According to Mayow, the respiration in 



