Fluid Pressure 105 



In honour of Robert Boyle, who first enunciated 

 the above law, it is called "Boyle's Law" 1 . It is 

 assumed that, during the performance of experiments 

 such as that just described, neither heating nor cooling of 

 the enclosed gas is allowed to take place, since, as will 

 be demonstrated later, these changes of temperature 

 will cause corresponding changes of volume indepen- 

 dently of those caused by the variations of pressure, 

 thus nullifying to some extent any deductions drawn 

 from the observations made. 



Exercise for Student. 



Try to deduce the second statement of Boyle's Law given above 

 from the observations quoted in the table. 



64. The gas used in our experiment was air, the 

 most easily procured, and therefore most convenient, 

 gas for our purpose. Similar observations would have 

 been obtained, however, had the gas enclosed in the 

 tube used been any other of the commonly occurring 

 gases. Thus, in the statements of the law given, the 

 word "gas" is used, and not "air", in order to show 

 the general applicability of the law to all gaseous 

 substances. 



It must not be inferred, however, that the law is 

 strictly applicable to the behaviour of all gases under 

 all conditions of temperature and pressure. An impor- 

 tant deviation is noted in the case of some gases when 

 they are submitted to considerable increase of pressure 

 at the ordinary temperature, the decrease of volume 

 corresponding to a given increment of pressure being 

 distinctly greater than that required in accordance with 



1 This law was independently discovered at a later date by the 

 French investigator, Mariotte, and hence is generally referred to on 

 the Continent as " Mariotte's Law "'. 



