96 Mayow 



So that clearly we must conclude that the air con- 

 tained in the glass has its elastic force diminished by 

 about one-fourth part, in consequence of the said 

 action produced by the spirit of nitre encountering 

 the iron. Hence it is unable to make the same resist- 

 ance as previously to the pressure of the atmosphere^ 

 and consequently the water underneath is impelled 

 upwards into the glass. 



Further, after the vapours in the said glass have 

 been as far as possible condensed and the water inside 

 does not rise any higher, let its height be indicated as 

 before by pieces of paper. Then let the iron be 

 lowered a second time into the vessel containing the 

 spirit of nitre, that action may be excited anew. But 

 that this may the better succeed, an ample supply of 

 spirit of nitre ought to be put into the vessel, or 

 rather two vessels containing spirit of nitre, and also two 

 small portions of iron, should be suspended in the glass. 

 When the water sinks anew about five finger-breadths 

 in consequence of the vapours produced, let the iron 

 as before be taken out of the vessel, and when this is 

 done the water will gradually rise in the glass, yet not so 

 quickly nor so far as the first time. For the water 

 which rose after the first action about six finger- 

 breadths, and far indeed above the height first marked, 

 will only rise after the second, even should it be more 

 intense, some two finger-breadths more or less. Nay^ 

 it will never rise to the mark from which it fell. If the 

 action be repeated a third time the result will be just 

 the same as in the second. 



Now it seems extraordinary that the water which, 

 after the effervescence first excited, was raised far above 

 the height from which it sank, should after the second 

 action, though brought about in the very same way, 

 not even recover its former height. For what are 



