64 GREAT MEN OF SCIENCE 



it was true within the accuracy obtainable at that time, and 

 within the possible limits of pressure. 



Among Boyle's numerous experiments are to be found 

 many containing important results in chemistry, relating to 

 the characteristic behaviour of various substances towards 

 one another; these researches became later the foundation of 

 chemical analysis. Examples are the detection of hydro- 

 chloric acid by precipitation with silver solution, of iron by 

 tincture of galls, of acids by means of paper dyed with veget- 

 able colouring matter. Boyle was altogether the first to pay 

 close attention to chemistry simply for the sake of know- 

 ledge, and not with the object of making gold, the philo- 

 sopher's stone, or an elixir of life. 



Edme Mariotte, born in Burgundy, was a priest. Prior of 

 a monastery near Dijon; but after being made a member of 

 the newly formed Academy in Paris as a result of his scientific 

 activity, he lived in Paris until his death. He proved himself 

 in many directions to be a thorough investigator. In par- 

 ticular, the behaviour of air at different pressures engaged 

 his attention, in connection with the observations of Guericke, 

 Toricelli, and Pascal. He also, like Boyle, arrived at the 

 discovery of the simple quantitative relationship between 

 pressure and volume, the 'law of Boyle or Mariotte.' His 

 publication appeared in 1676, sixteen years later than the 

 almost exactly similar experiments of Boyle; but Mariotte 

 was the first to make at the same time a fundamental and im- 

 portant application of the law, in his essay 'Sur la nature 

 de I'air.' He calculated quite correctly the decrease in the 

 pressure of the atmosphere with increase in height, making 

 use of Guericke's discovery that the density of the air must 

 diminish as we go upwards. He therefore carried out the 

 calculation in small steps of height. In going upwards, the 

 density of the air is reduced as a consequence of reduced 

 pressure, and hence equal masses of air occupy a less volume, 



