But modern discoveries in radioactivity 2 are in favour of the existence of the atom, although they lead to the belief that the atom is not so eternal and unchangeable a thing as Dalton and his predecessors imagined, and in fact, that the atom itself may be subject to that eternal law of growth and decay of which Lucretius speaks.
It requires a radium salt of high radioactivity to be at all comparable in effectiveness with a good water-dropper.
Their method of measuring the radioactivity is as follows (48) : A wire not exceeding 1 mm.
The radioactivity is denoted by A, and A = signifies that the potential of the dissipation apparatus fell I volt in an hour per metre of wire introduced.
(For the significance of this fact see Radioactivity.) The richest known source is thorianite, which consists mainly of thorium oxide, and contains 9.5 cc. of helium per gram.
Turning to the study of radioactivity, he noticed its association with the minerals which yield helium, and in support of the hypothesis that that gas is a disintegration-product of radium he proved in 1903 that it is continuously formed by the latter substance in quantities sufficiently great to be directly recognizable in the spectroscope.
He was distinguished as the discoverer of radioactivity, having found in 1896 that uranium at ordinary temperatures emits an invisible radiation which in many respects resembles Rntgen rays, and can affect a photographic plate after passing through thin plates of metal.
Curie, regarding radioactivity - i.e.
In connexion with the modern study of radioactivity, the electroscope has become an instrument of great usefulness, far outrivalling the spectroscope in sensibility.
This research opened a way of approach to the phenomena of radioactivity, and the history of the steps by' hich P. Curie and Madame Curie were finally led to the discovery of radium is one of the most fascinating chapters in the history of science.
The study of radium and radioactivity led before long to the further remarkable knowledge that these so-called radioactive materials project into surrounding space particles or corpuscles, some of which are identical with those projected from the cathode in a high vacuum tube, together with others of a different nature.
The study of radioactivity was pursued with great ability not only by the Curies and A.