A NEW POSSIBLE SOURCE OF COSMICAL ENERGY Hydrogen, in Aston's mass spectrograph, appears to have an atomic mass of 1.008 (0-16), precisely as found by the chemists. Hydrogen, however, is unique among the elements in having no electrons but merely one proton in its nucleus. In all other atomic nuclei there are electrons packed close to the protons, and this close packing of charges of opposite sign is expected, by electrical theory, to influence the electromagnetic mass of the complex by an amount dependent on the closeness of packing. If we could build a helium atom from the materials which are correctly furnished by four hydrogen atoms, there would ensue a loss of mass of about 0.8 per cent., since the atomic weight of helium is 4.00. This mass, however, can not be destroyed, but must appear, according to the relativity theory, as an equivalent amount of energy. The quantity of energy concerned in the transformation of 1 gram of hydrogen to helium, namely 8 milligrams, or about the weight of one fifth of a postage stamp, corresponds to what, as electrical energy at ten cents per kilowatt hour, would cost $20,000.

If such a synthesis of helium from hydrogen may be supposed to be going on in the sun, we have a much needed explanation of the sun's present brightness at his known old age.

EXPERIMENTAL UTILIZATIONS OF ALPHA-PARTICLES IN INVESTIGATION

The alpha-particles expelled from radioactive elements are by far the most energetic entities with which we are yet acquainted. The swifter kinds have, for unit mass, an energy of motion 400 million times greater than that of a rifle bullet. Being helium nuclei without circumambient planetary electrons, they are very small, and readily shoot through atoms, knocking out their extranuclear electrons right and left. The damaged atoms soon pick up other electrons to fill the gaps, and thus suffer no permanent change. Alpha-particles pass through thin glass, leaving no hole. Very occasionally, an alpha-particle will make a bullseye collision with the nucleus of an atom. The consequence of this collision, in the case of nuclei of some light atoms, is that the nucleus struck is disintegrated, with the expulsion of a single, swift-moving proton. The experiment succeeds in the case of B, N, F, Na, Al, and P nuclei. In the case of aluminium, Rutherford found that the single protons expelled have an energy of motion that is 40 per cent. greater than that of the alpha-particle missile that struck the atom. What remains of the aluminium nucleus is still under investigation, but it is permanently changed and is certainly no longer aluminium. Thus, in transmuting an element, we obtain free energy. The alchemists expressed this allegorically when they identified the philosopher's stone, which would transmute metals,

with the elixir of life, a source of ever fresh life or energy. Our enthusiasm for this transmutation is duly restrained by the knowledge that only about two per million alpha-particles make bullseyes on the aluminium nuclei.

In the case of the heavier atoms with their more highly charged nuclei, the alpha-particle, of the speed hitherto at our disposal, apparently loses too much energy in the approach to be able to effect disintegration of the nucleus. Its path is sometimes bent back in a large angle deflection, by an elaborate study of which in the case of gold the existence of the minute, positively charged nucleus of atoms was first established. The nuclear charges of gold, platinum, silver and copper have each been directly evaluated by this method, and agree with the atomic numbers of these atoms to 1 per cent., the known value of the experimental error.

THE DURATION AND POSSIBLE REPETITIONS OF GEOLOGICAL TIME

The unchanging and, so far as all experiment goes, unchangeable spontaneous disintegration of heavy atomic nuclei has geological interests both in view of the time periods involved and also of the energy emitted in the process. Thorium disintegrates into thorium-lead, which is stable, at a rate which we have been able to ascertain. The "range" or distance travelled through matter by the expelled alpha-particles is strictly related to the rate of the various disintegrations, and such ranges and rates have ever remained constant for thorium and its descendants as evidenced by the constancy of the diameters of the range "halos" surrounding microscopic thorium inclusions in rocks of various ages. The diameters of these halos agree, also, with the ranges in air of the alpha-particles as studied to-day, and so the thorium clock has ever run at the same rate. Some thorium minerals contain lead whose measured atomic weight shows that it has practically all been derived from the decay of thorium atoms. From the ratio of the number of thorium atoms remaining to the number of those originally present, many of which are now represented by lead atoms which they produced, one can compute the age of the mineral, which thus gives a date to early paleozoic times of 150 million years back. Similar calculation from uranium minerals gives a period over 900 million years, but there is reason to believe that the uranium clock formerly ran fast, or, rather, that it appeared to run fast owing to the former presence of a third isotope of uranium, now almost extinct, of speedier rate of decay than what to-day we call U-1.

Rock analysis shows that, assuming percentage composition similar to that on the surface, there is enough radioactive material

in a depth of only 12 miles of the earth's crust to supply by its daily disintegration all the heat the earth radiates daily into space. If an appreciable amount of radioactive material exists below this depth, as seems certain, then heat must slowly be accumulating within the earth's non-conducting crust. Eventually, therefore, if no compensating heat-absorbing process is taking place within, an unstable state will be reached when the underlying incandescent material will perforce evert itself to the exterior and there disburden itself of its accumulated heat by radiation into space at a very rapid rate proportional to the fourth power of the temperature. This is the earth's incandescent epoch. When the crust has cooled down again sufficiently, a new geological epoch of perhaps 200 million years may begin, to be followed in turn by another incandescent epoch, and so on, alternately, but more and more slowly, until the radioactive materials, if not regenerated, have by disintegration lost their available energy. This alternation the Brahmans have symbolized in their cosmogony as the indrawing and outbreathing.of the breath of Brahma.

THE PROGRESS OF SCIENCE