Lord Rayleigh, Sir William Ramsay 181 



only led to perfecting an established theory in an important 

 detail. 



The new era begins with Lord Rayleigh 's discovery of 

 argon. The research which led to it was originally under- 

 taken with a view to testing the hypothesis of William Prout 

 (1786-1850), a London doctor, according to whom the atomic 

 weights of all chemical elements are exact multiples of that 

 of hydrogen. In the course of an accurate determination of 

 the density of nitrogen it was found that, when the gas is 

 prepared from air by removing all other known constituents, 

 it has a density half per cent, greater than when it is obtained 

 directly from ammonia. Rayleigh then drew the conclu- 

 sion that the discrepancy was due to some unknown body, 

 probably a new gas in the atmosphere heavier than nitro- 

 gen. While the research was advancing successfully, William 

 Ramsay joined the investigation, and the final results were 

 published by Rayleigh in conjunction with him. 



Sir William Ramsay (1852-1916) then entered into that 

 period of his activity in which discoveries rapidly succeeded 

 each other. Sir Henry Miers drew his attention to a certain 

 mineral which was known to give out an inert gas when 

 dissolved in an acid. This gas was supposed to be nitrogen, 

 but Miers thought it might turn out to be argon. Ramsay 

 extracted the gas, examined it with a spectroscope, and to 

 his surprise found the bright yellow line which appears so 

 brilliantly in the light emitted all round the edge of the 

 sun and in its protuberances. The gas proved, therefore, 

 to be identical with the one spectroscopically discovered 

 many years previously by Sir Norman Lockyer, and named 

 by him " helium." Subsequently, by applying the process 

 called " fractional distillation " to liquid air, Ramsay could 

 isolate three additional elements : krypton, xenon, and 

 neon. 



In the meantime, experiments on the discharge of 

 electricity through gases had made rapid progress. His 

 experiments with the radiometer had led Crookes to intro- 

 duce great improvements in the construction of the mercury 

 pumps used to obtain high vacua in glass vessels. By sending 

 electric currents of high potentials through such vessels, 

 Crookes investigated the vivid phosphorescent luminosity 



