SIR WILLIAM RAMSAY—MOUREU. 535 
opportunity presented itself to him; he exploited it with admirable 
and masterful decision. 
Early in 1895 Ramsay learned, through a letter from Sir Henry 
Miers, that Hillebrand, chemist in the United States Geological Sur- 
vey, had observed, while treating a uraniferous mineral, cleveite, 
with boiling sulphuric acid, the giving off of a gas which appeared 
to him to be nitrogen. The effect produced on Ramsay by this news 
was entirely characteristic of his scientific temperament. Many 
chemists, while finding the observation interesting, would have put 
off the study of the subject until later, when they might have more 
leisure. Ramsay, on receipt of the letter from Sir Henry Miers, 
called the laboratory aid and dispatched him immediately to the 
shops of the mineral merchants of London to buy all the cleveite 
that he could find. The cleveite arrived toward noon; before night 
it had been treated and the gas collected. During the two following 
days the known gases, except argon, which it had been expected 
would be found, were eliminated and the residue introduced into a 
spectrum tube. The spectrum of argon was not observed. There 
were few lines; one of these—yellow—was very brilliant. It was 
thought at first to be the line of sodium, present, perhaps, in the cor- 
roded electrodes. But Ramsay laughed at the idea; he was not in 
the habit of using dirty spectrum tubes, and, besides, he had made 
the tube himself. A comparison spectrum of sodium was observed 
simultaneously. The two lines were distinct and in no way super- 
posed. It was then beyond doubt that it was a new gas, and the 
hypothesis was advanced that it might be helium. 
Helium was that element, still unknown on the earth, whose ex- 
istence in the sun was known through a spectroscopic observation 
carried out by the French astronomer Janssen at the time of the solar 
eclipse of the year 1868, and the subsequent suggestions of the En- 
glish physicists Frankland and Lockyer. Was this new gas of Ram- 
say’s helium, or was it not? The answer was not long in coming. 
The spectrum tube was sent to Sir William Crookes, who measured 
with great care the wave length of the yellow line and found it 
identical with’ that of the solar line of helium. Scarcely a week had 
passed since Ramsay had received the letter from Sir Henry Miers. 
At the general reunion of the Chemical Society in March, 1895, 
the discovery of terrestrial helium in the gases from cleveite was an- 
nounced. Its molecular weight was 4, and a study of the specific 
heat indicated that the molecule was monatomic, like that of argon, 
which it also resembled through its complete chemical inertness. 
During the two following years Ramsay hunted carefully for 
other sources of argon and helium. Argon and helium were found 
in certain mineral waters, those of Cauterets among others; to-day 
