56 PHYSICAL SCIENCE 



attainable accuracy, phenomena already known 

 to science. Since the days of Cavendish, the 

 composition of the air had been looked upon as 

 an ascertained fact ; a certain proportion had 

 been shown to be oxygen, varying amounts of 

 carbonic acid and aqueous vapour were known to 

 be present, while the remainder, as the result of 

 careful investigation, was supposed to be nitrogen. 

 Cavendish himself knew, so accurate was his 

 work, that any undetected residue could not 

 exceed the yluth part. But in the course of a 

 long series of experiments, undertaken to deter- 

 mine afresh the densities of the principal gases. 

 Lord Rayleigh detected a slight difference in the 

 density of nitrogen as prepared from ammonia 

 and as extracted from the air. This difference, 

 amounting at first to about o. i per cent., was 

 increased on subsequent more careful examina- 

 tion to nearly a half per cent. It was clear that 

 the gases prepared by these two methods were 

 not identical, and that some hitherto unknown 

 body was responsible for the complication. The 

 existence of this new body, the inert gas now 

 known as argon, was announced by Rayleigh and 

 Ramsay in 1894, and shortly afterwards it was 

 isolated from its companions. 



Argon is slightly more soluble in water than 

 nitrogen, hence a rather larger proportion of it 

 than might be expected is found in rain water. 

 It is also contained to a small extent in the gases 

 liberated fromi certain thermal springs. Traces 

 of three other gases, neon, krypton, and xenon, 

 which much resemble argon In chemical properties, 

 have been detected in the atmosphere. The total 

 amount of these three substances is almost im- 



