92 INHERITANCE IN ANIMALS 



gas remaining. Cavendish was not sure what this small 

 bubble of gas was. It might have been introduced by 

 accident during the manipulations, but he said that if this 

 bubble represented some constituent of the atmosphere, 

 which was neither oxygen nor nitrogen, the amount of it 

 was about one volume to every hundred volumes of 

 atmospheric nitrogen. For a whole century no one 

 seems to have repeated Cavendish's experiment with 

 such care as to make sure about this residual bubble. 

 Other means were adopted for the analysis of the air, 

 and since these did not show the presence of any gas 

 besides oxygen, nitrogen, and carbonic acid, Cavendish's 

 residual bubble was forgotten or neglected. 



But Lord Rayleigh and Sir William Ramsay, when 

 they took counsel together how they might account for 

 the peculiarity of atmospheric nitrogen, remembered this 

 bubble ; and Sir William Ramsay determined to find out 

 what it really contained. By a variety of ingenious 

 methods we cannot stop to consider, he did find out. He 

 found that about one volume in every hundred of the gas 

 in the atmosphere which had been regarded as pure 

 nitrogen was not nitrogen at all, but was formed of a 

 group of elementary gases, the chief of which is that 

 called argon. Argon is about one-and-a-half times as 

 heavy as nitrogen, so that the presence of about one 

 volume of argon in every hundred volumes of the gas 

 called atmospheric nitrogen renders this gas about one- 

 half per cent, heavier than pure nitrogen, and so accounts 

 for the discrepancy between Lord Rayleigh's two groups 

 of weighings. 



The discovery of argon was, therefore, directly due to 

 a refusal to replace the variable and discordant experience 

 of the weight of nitrogen by an ideal uniformity based on 

 the mean of the actual experiences. If Lord Rayleigh had 



