118 



Anniversary Meeting. 



[Nov. 30, 



with Ramsay, who had joined him in the work; but no details had 

 then been published. They had succeeded in isolating the new con- 

 stituent by extracting all the four previously known constituents 

 (oxygen, nitrogen, aqueous vapour, carbonic acid) from air, and they 

 were energetically at work with a view to discovering its properties. 

 I concluded my last year's address by expressing the hope that their 

 work would give us, "before the next anniversary meeting of the 

 Royal Society, much knowledge of the properties, both physical and 

 chemical, of the hitherto unknown and still anonymous fifth constituent 

 of our atmosphere." That hope, as you all know, has been splendidly 

 fulfilled. They early discovered a name for it, Argon, because exhaus- 

 tive chemical investigation gave them no evidence of its chemical 

 combination with any other known element. They found its density 

 to be very high, 20 (that of oxygen being called 16), and the ratio of 

 its specific heats If. Olszewski, experimenting on a specimen sent 

 to him by Ramsay, succeeded in liquefying it, and found its critical 

 pressure to be 50'6 atmospheres and its critical temperature —121°. 

 These results were communicated, in a joint paper by Rayleigh 

 and Ramsay to the Royal Society at a memorable meeting, held 

 (January 31) in the theatre of the University of London, because our 

 ordinary meeting room was not large enough to contain all who 

 wished to hear it. It will be gratifying to Fellows of the Royal 

 Society to know that the Smithsonian Institution of Washington 

 gave to Lord Rayleigh and Professor William Ramsay the first 

 Hodgkins' prize for their ' Memoir on Argon : a new constituent of 

 the Atmosphere.' This memoir had been communicated to Wash- 

 ington before the en^ of December, 1894. 



Since the dates of those first communications much work has been 

 done by various observers on the spectrum analysis of argon. In a 

 communication by Rayleigh to the recent meeting of the British 

 Association, we find a very accurate determination of its refractive 

 index and its viscosity. Ramsay, in trying for clues to compounds 

 of argon, had his attention called by Mr. Miers of the British Museum 

 to a paper by Hillebrande, telling that cleveite (a rare Norwegian 

 mineral which consists chiefly of uranate of lead) gives out 2 per 

 cent, of a gas, supposed to be nitrogen, when warmed with weak 

 sulphuric acid. Ramsay, thinking the so-called nitrogen might turn 

 out to be argon, experimented on the mineral. He found that the 

 gas evolved, by heating it in sulphuric acid, contained a trace of 

 nitrogen, which he removed by the Cavendish process of sparking 

 with oxygen in presence of alkaline liquor. The residue was proved 

 by the spectrum test to contain argon, but to contain also another 

 gas, not argon, showing itself by a brilliant yellow line. This line 

 was identified by Crookes as the " helium line," discovered thirty 

 years ago by Lockyer, who, finding it to have been not discovered in 



