VI.Binary Systems.
VI.Binary Systems.
VI.Binary Systems.
The theory affords a rational explanation of the origin of binary stars. Binary stars, in so far as regards their motion, follow also, of course, as a consequence, from the gravitation theory. If two bodies come into grazing collision, “they will,” says SirWilliam Thomson, “commence revolving round their common centre of inertia in long elliptic orbits. Tidal interaction between them will diminish the eccentricities of their orbits, and, if continued long enough, will cause them to revolve in circular orbits round their centre of inertia.”[19]This conclusion was pointed out many years ago by Dr. Johnstone Stoney.
VII.Sudden Outbursts of Stars.
VII.Sudden Outbursts of Stars.
VII.Sudden Outbursts of Stars.
The case of a star suddenly blazing forth and then fading away, such as that observed by Tycho Brahe in 1572, may be accounted for by supposing that the star had been struck by one of the dark bodies—an event not at all impossible, or even improbable. In some cases of sudden outbursts, such as that of Nova Cygni, for example, the phenomenon may result from the star encountering a swarm of meteorites. The difficulty in the case of Nova Cygni is to account for the very sudden decline of its brilliancy. This might, however, be explained by supposing that the outburst of luminosity was due to the destruction of the meteorites, and not to any great increase of heat produced in the star itself. A swarm of meteorites converted into incandescent vapour would not be long in losing its brilliancy.
Mr. Lockyer thinks that the outburst was produced by the collision of two swarms of meteorites, and not by the collision of the meteorites with a previously existing star.[20]
Amongst the millions of stars occupying stellar space catastrophes of this sort may, according to the theory, be expected sometimes to happen, although, like the collisions which originate stars themselves, they must, doubtless, be events of but rare occurrence.
VIII.Star Clusters.
VIII.Star Clusters.
VIII.Star Clusters.
A star cluster will result from an immensely widespread nebula breaking up into a host of separate nuclei, each of which becomes a star. The irregular manner in which the materials would, in many cases, be widely distributed through space after collision would prevent a nebula from condensing into a single mass. Subordinate centres of attraction would be established, as was long ago shown by Sir William Herschel in his famous memoir on the formation of stars;[21]and around these the gaseous particles would arrange themselves and gradually condense into separate stars, which would finally assume the condition of a cluster.
IX.Age of the Sun’s Heat: a Crucial Test.
IX.Age of the Sun’s Heat: a Crucial Test.
IX.Age of the Sun’s Heat: a Crucial Test.
When we come to the question of the age of the sun’s heat, and the length of time during which that orb has illuminated our globe, it becomes a matter of the utmost importance which of the two theories is to be adopted. On the age of the sun’s heat rests the whole question of geological time. A mistake here is fundamental. If gravitation be the only source from which the sun derived its heat, then lifeon the globe cannot possibly date farther back than 20,000,000 years; for under no possible form could gravitation have afforded, at the present rate of radiation, sufficient heat for a longer period. It will not do to state in a loose and general way, as has been frequently done, that the sun may have been supplying our globe with heat at its present rate for 20,000,000 or 100,000,000 years, for gravitation could have done no such thing; a period of 20,000,000, not 100,000,000, years is the lowest which is admissible on that theory. Not even that length of time would be actually available; for this period is founded on Pouillet’s estimate of the rate of solar radiation, which has been proved by Langley to be too small, the correct rate being 1·7 times greater. “Thus,” as says Sir W. Thomson, “instead of Helmholtz’s 20,000,000 years, we have only 12,000,000.” But the 12,000,000 years would not in reality be available for plant and animal life; for undoubtedly millions of years would elapse before our globe could become adapted for either flora or fauna. If there is no other source of heat for our system than gravitation, it is doubtful if we can calculate on much more than half that period for the age of life on the earth. Professor Tait probably over-estimates the time when he affirms “that 10,000,000 years is about the utmost that can be allowed, from the physical point of view, for all the changes that have taken place on the earth’s surface since vegetable life of the lowest known form was capable of existing there.”[22]And thisis certainly about all that can ever be expected from gravitation; mathematical computation has demonstrated that it can give no more. The other theory, founded on motion in space—a cause as real as gravitation—labours under no such limitation. According to it, so far at least as regards the store of energy which may have been possessed by the sun, plant and animal life may date back, not to 10,000,000 years, but to a period indefinitely more remote. In fact, there is as yet no known limit to the amount of heat which this cause may have produced; for this depended upon the velocities of the two bodies at the moment prior to collision, and what these velocities were we have no means of knowing. They might have been 500 miles a second, or 5,000 miles a second, for anything which can be shown to the contrary. Of course I by no means affirm that it is as much as 100,000,000 years since life began on our earth; but I certainly do affirm that, in so far as a possible source of the sun’s energy is concerned, life may have begun at a period as remote.