The heavier ones, such as carbon and iron, would be repelled as strongly by the electric forces, but they would be more strongly pulled back by the gravitative forces, thus producing a much slower separation between them and the head of the comet.
"A Text-Book of Astronomy"
George C. Comstock
To deduce the laws of the heavenly motions, we require not only to know the law of a rectilineal and that of a gravitative force, but the existence of both these forces in the celestial regions, and even their relative amount.
"A System Of Logic, Ratiocinative And Inductive (Vol. 1 of 2)"
John Stuart Mill
The prolate or lemon-like shape is caused by the gravitative pull of the earth, balanced by the centrifugal whirl.
"Pioneers of Science"
Oliver Lodge