68 PRESSURE OF LIGHT 



parts of the gas chamber. In the mixtures so 

 formed a ranged from 0*005 to ' 2 - 



The observed pressure differences were of the 

 order of a millionth of a dyne, and different ob- 

 servations with the same gas agreed with each 

 other within about 10 per cent. The values calcu- 

 lated from aE, when corrected in various ways 

 into which we cannot enter, agreed usually within 

 about 20 per cent, with the observed values. 



When we realize how exceedingly minute is a 

 pressure of a millionth of a dyne per centimetre 

 a million millionth of an atmosphere we can only 

 admire the experimental skill which succeeded in 

 making consistent measurements and thereby 

 proving that there is at least an approximate 

 agreement between theory and experiment. 



