It is possible, by considerations analogous to those set forth above in other cases, to arrive at an idea of the total number of particles per second expelled by one gramme of radium; Professor Rutherford in his most recent evaluation finds that this number approaches 2.5 x 10^{11}.[41] By calculating from the atomic weight the number of atoms probably contained in this gramme of radium, and supposing each particle liberated to correspond to the destruction of one atom, it is found that one half of the radium should disappear in 1280 years;[42] and from this we may conceive that it has not yet been possible to discover any sensible loss of weight.  Sir W. Ramsay and Professor Soddy attained a like result by endeavouring to estimate the mass of the emanation by the quantity of helium produced.

[Footnote 41:  See Radioactive Transformations (p. 251).  Professor Rutherford says that “each of the alpha ray products present in one gram of radium product (sic) expels 6.2 x 10^{10} alpha particles per second.”  He also remarks on “the experimental difficulty of accurately determining the number of alpha particles expelled from radium per second.”—­ED.]

[Footnote 42:  See Rutherford, op. cit. p. 150.—­ED.]

If radium transforms itself in such a way that its activity does not persist throughout the ages, it loses little by little the provision of energy it had in the beginning, and its properties furnish no valid argument to oppose to the principle of the conservation of energy.  To put everything right, we have only to recognise that radium possessed in the potential state at its formation a finite quantity of energy which is consumed little by little.  In the same manner, a chemical system composed, for instance, of zinc and sulphuric acid, also contains in the potential state energy which, if we retard the reaction by any suitable arrangement—­such as by amalgamating the zinc and by constituting with its elements a battery which we cause to act on a resistance—­may be made to exhaust itself as slowly as one may desire.

There can, therefore, be nothing in any way surprising in the fact that a combination which, like the atomic combination of radium, is not stable—­since it disaggregates itself,—­is capable of spontaneously liberating energy, but what may be a little astonishing, at first sight, is the considerable amount of this energy.

M. Curie has calculated directly, by the aid of the calorimeter, the quantity of energy liberated, measuring it entirely in the form of heat.  The disengagement of heat accounted for in a grain of radium is uniform, and amounts to 100 calories per hour.  It must therefore be admitted that an atom of radium, in disaggregating itself, liberates 30,000 times more energy than a molecule of hydrogen when the latter combines with an atom of oxygen to form a molecule of water.

We may ask ourselves how the atomic edifice of the active body can be constructed, to contain so great a provision of energy.  We will remark that such a question might be asked concerning cases known from the most remote antiquity, like that of the chemical systems, without any satisfactory answer ever being given.  This failure surprises no one, for we get used to everything—­even to defeat.