<P> There is evidence that Emanuel Swedenborg first proposed parts of the nebular hypothesis in 1734 . Immanuel Kant, familiar with Swedenborg's work, developed the theory further in 1755, publishing his own Universal Natural History and Theory of the Heavens, wherein he argued that gaseous clouds (nebulae) slowly rotate, gradually collapse and flatten due to gravity, eventually forming stars and planets . </P> <P> Pierre - Simon Laplace independently developed and proposed a similar model in 1796 in his Exposition du systeme du monde . He envisioned that the Sun originally had an extended hot atmosphere throughout the volume of the Solar System . His theory featured a contracting and cooling protosolar cloud--the protosolar nebula . As this cooled and contracted, it flattened and spun more rapidly, throwing off (or shedding) a series of gaseous rings of material; and according to him, the planets condensed from this material . His model was similar to Kant's, except more detailed and on a smaller scale . While the Laplacian nebular model dominated in the 19th century, it encountered a number of difficulties . The main problem involved angular momentum distribution between the Sun and planets . The planets have 99% of the angular momentum, and this fact could not be explained by the nebular model . As a result, astronomers largely abandoned this theory of planet formation at the beginning of the 20th century . </P> <P> A major critique came during the 19th century from James Clerk Maxwell (1831 - 1879), who maintained that different rotation between the inner and outer parts of a ring could not allow condensation of material . Astronomer Sir David Brewster also rejected Laplace, writing in 1876 that "those who believe in the Nebular Theory consider it as certain that our Earth derived its solid matter and its atmosphere from a ring thrown from the Solar atmosphere, which afterwards contracted into a solid terraqueous sphere, from which the Moon was thrown off by the same process". He argued that under such view, "the Moon must necessarily have carried off water and air from the watery and aerial parts of the Earth and must have an atmosphere". Brewster claimed that Sir Isaac Newton's religious beliefs had previously considered nebular ideas as tending to atheism, and quoted him as saying that "the growth of new systems out of old ones, without the mediation of a Divine power, seemed to him apparently absurd". </P> <P> The perceived deficiencies of the Laplacian model stimulated scientists to find a replacement for it . During the 20th century many theories addressed the issue, including the planetesimal theory of Thomas Chamberlin and Forest Moulton (1901), the tidal model of Jeans (1917), the accretion model of Otto Schmidt (1944), the protoplanet theory of William McCrea (1960) and finally the capture theory of Michael Woolfson . In 1978 Andrew Prentice resurrected the initial Laplacian ideas about planet formation and developed the modern Laplacian theory . None of these attempts proved completely successful, and many of the proposed theories were descriptive . </P>

Compare and contrast nebular hypothesis and protoplanet hypothesis