Modern science : a general introduction / by J. Arthur Thomson.

  • Thomson, J. Arthur (John Arthur), 1861-1933.
Date:
[1929]
Catalogue details

Licence: In copyright

Credit: Modern science : a general introduction / by J. Arthur Thomson. Source: Wellcome Collection.

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    arose as one of the knots on the arms of a huge twisted nebula. The other knots on the arms became the other planets, and perhaps the earth knot was originally a double knot, including the moon from the very first. It is possible that the nebulous arms were drawn out from the gaseous sun by the tidal attraction of a passing star; so that in a somewhat fanciful way we may think of the earth and the planets having two parents, the one being the sun, the other a great unknown. We should notice here that our present- day sun sometimes shoots out flaming solar prominences ” to heights of 100,000 miles, and some authorities would multiply this figure by three. These are often well seen when there is a total eclipse of the sun. The theory is that on the solar arms or out-drawn swirling gaseous masses there arose at intervals the condensations or knots that we have spoken of, and that further in¬ gathering of each of these knots formed the liquid or solid cores of the future planets, including the earth. As the condensations continued, each core gathered in by gravity what was left of the huge arms between the knots, besides immense quantities of fine dust-like particles which have received the long name planetesimals.” In some such way arose the separate planets, with our earth amongst them. Venus and Mercury are nearer to the sun ; Mars, Jupiter, Saturn, Uranus, and Neptune are farther away from the sun. Between Mars and Jupiter are the minor planets or asteroids, the largest probably not exceeding 300 miles in diameter, and these may be residues that were not con¬ centrated into one body. No doubt these theories are beset by many uncertainties and difficulties, but there is general agreement among astronomers that our solar system arose from a vast nebulous mass, whose centre formed our present sun, while out-lying secondary nebulae, which we have spoken of as “ arms,” were somehoiv drawn out, and then somehow condensed into separate planets, each revolving on its own orbit, and each with its own rate of rotation on its axis. So we trace the earth back to its parent the sun, or more accurately, to the nebula whose condensed centre eventually became the sun we know. But this inevitably raises the next question : Where did the solar nebula come from ? The usual answer is to point to some of the nebulae ob¬ servable in the heavens to-day, especially to what are