We can picture such a mass, in imagination, tumbling end over end in its orbit so as to present at one moment the broad sides of both bells, together with their connecting neck, toward the sun, and, at the same time, toward the observer on the earth, and, at another moment, only the end of one of the bells, the other bell and the neck being concealed in shadow.  In this way the successive gain and loss of sixfold in the amount of light might be accounted for.  Owing to the great distance the real form of the asteroid is imperceptible even with powerful telescopes, but the effect of a change in the amount of reflecting surface presented produces, necessarily, an alternate waxing and waning of the light.  As far as the fluctuations are concerned, they might also be explained by supposing that the shape of the asteroid is that of a flat disk, rotating about one of its larger diameters so as to present, alternately, its edge and its broadside to the sun.  And, perhaps, in order completely to account for all the observed eccentricities of the light of Eros, the irregularity of form may have to be supplemented by certain assumptions as to the varying reflective capacity of different parts of the misshapen mass.

The invaluable Harvard photographs show that long before Eros was recognized as an asteroid its light variations had been automatically registered on the plates.  Some of the plates, Prof.  E.C.  Pickering says, had had an exposure of an hour or more, and, owing to its motion, Eros had formed a trail on each of these plates, which in some cases showed distinct variations in brightness.  Differences in the amount of variation at different times will largely depend upon the position of the earth with respect to the axis of rotation.

Another interesting deduction may be made from the changes that the light of Eros undergoes.  We have already remarked that one of the larger asteroids, and the one which appears to the eye as the most brilliant of all, Vesta, has been suspected of variability, but not so extensive as that of Eros.  Olbers, at the beginning of the last century, was of the opinion that Vesta’s variations were due to its being not a globe but an angular mass.  So he was led by a similar phenomenon to precisely the same opinion about Vesta that has lately been put forth concerning Eros.  The importance of this coincidence is that it tends to revive a remarkable theory of the origin of the asteroids which has long been in abeyance, and, in the minds of many, perhaps discredited.

This theory, which is due to Olbers, begins with the startling assumption that a planet, perhaps as large as Mars, formerly revolving in an orbit situated between the orbits of Mars and Jupiter, was destroyed by an explosion!  Although, at first glance, such a catastrophe may appear too wildly improbable for belief, yet it was not the improbability of a world’s blowing up that led to a temporary abandonment of Olbers’s bold theory.  The great French mathematician Lagrange investigated the explosive force “which would be necessary to detach a fragment of matter from a planet revolving at a given distance from the sun,” and published the results in the Connaissance des Temps for 1814.