The masses of Encke's comet and the comet of Taurus determined by M. Babinet– Objections to this method of determination.

We have thus a determination of cometary masses deduced from the reciprocal disturbances exercised by comets and the planets on one another. It shows that comets have extremely small masses, since, greatly disturbed themselves in their course when they approach a planet, they appear never to have exercised any disturbing influence upon the movements of the planet itself. But, from the value found for the mass of Lexell's comet–a value which, however, is only a maximum limit–it may be seen how far a comet is from being considered a visible nonentity (rien visible), to make use of the forcible expression of M. Babinet. The 5,000th part of the mass of the terrestrial globe is equivalent to the sixtieth part of the mass of the moon, a quantity, it will be agreed, far from negligible.

For the justification of his expression M. Babinet has relied upon the following optical considerations. He has called attention to the known fact that stars of exceedingly faint light may be seen through cometary nebulosities without their light losing any of its intensity.