Essay on Tidal Theories of James and Jeffrey's

Sir James Jeans and Prof. Harold Jeffrey's, the British scientists put forward a tidal theory in 1919 to meet the objections against Laplacian hypothesis and the shortcomings of the tidal theory of Chamberlin and Moulton.

Jeans and Jeffrey's suggested the approach of a passing star which produced the tidal effect. It may be pointed out that Prof. Harold Jeffrey's modified this theory in 1929 in his own way. His modified theory was also full of many shortcomings.

It may be pointed out that the passing star was much larger than the sun in size and mass. Under the gravitational pull of the passing star the sun would be deformed into a lobate body in the direction of the former.

The passing star raised enormous tides and pulled outward gaseous filament of solar matter as the star approached nearer and nearer. By the time the star reached the farthest position, the filament had so much enlarged itself that ultimately it was detached from the sun.

The filament being so massive, it is able to maintain itself without dispersal. Gravity would cause the formation of knots. The passing star gives a rotary motion to the filament. It is noteworthy that the filament was considered to be the building material of planets of the solar system.

The filament was given a rotary motion by the passing star. As the star passed into space, the filament was left behind in the gravitational range of the sun. So the filament revolves round the sun. As the star recedes, the filament breaks up and the planets condensed out of it.

When the star was nearest the sun, its pull was greatest, so the filament would naturally be thickest in the middle. The planets, therefore, would be larger than those at the outer ends of the filament.

In this way the solar system came into existence. The planets thus formed retain the angular momentum imparted by the passing star. The planets revolve round the sun in the same plane which contained the sun and the passing star.

As regards the origin of satellites, the tidal theory of James Jeans suggests that the planets which were bigger in size would remain in gaseous state for longer time and they took longer time to cool.

On the contrary, the planets that were smaller in size took less time to cool and condense. The gravitational pull of the sun was more effective in raising small filaments from the outer surface of the bigger planets due to their gaseous form.

Whereas the larger numbers of satellites were formed from the bigger planets, the smaller planets could produce lesser number of satellites. No satellites were formed from small planets located at the extreme end of the planetary system because they took very little time to come into solid form.

By the time the satellites were formed, their parent-planets were cooled to a liquid state. Therefore it is possible that satellites were formed as liquid masses.

According to this theory, the original orbits of the planets were eccentric, not circular, but the intruding star by its tidal effect might have scattered solar matter round the sun in addition to raising the filament.

The resistance offered by the scattered matter would have reduced eccentricity of the planetary orbits and made them circular.

Criticism:

(i) Because of the vastness of the distances among stars in the universe, the fact of encounter of a star with the sun is a remote possibility.

(ii) Raising a filament of matter by a passing star may be possible, but the imparting of a revolutionary motion to the filament or its constituents is improbable.

(iii) The question of angular momentum, i.e. the great distance of the outer planets from the sun is difficult to explain.

(iv) The sun at some stage in its life history must have been greatly swollen due to nuclear reactions. The swollen condition would have been there until the nuclear fuel was exhausted.

During this stage the possibility of an encounter with an intruding star was greater. This may be offered as an explanation for the great distance of the planets from the sun. However, it must be presumed that the sun was of its present size during 80-90 per cent of its life.

(v) According to the tidal theory the earth developed a liquid core soon after its gaseous origin. The earth is supposed to have cooled from the expansion of the gases and radiation of heat from the outer crust.

Further cooling caused solidification and zoning of the earth's matter in accordance with densities. It was Jeffrey's assumption that the above mentioned changes occurred in a short period of time.

However, Jeffreys wrote to Gutenberg in 1951 that his tidal theory that was propounded in ' 1929 was quite wrong in some places and needed modification.

It may be mentioned that Sir Harold Jeffreys introduced certain modifications in this theory in 1929, so the names of both, James Jeans and Jeffreys are associated with the tidal hypothesis.