Discussions on climate and cosmology / by James Croll.

  • James Croll
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: Discussions on climate and cosmology / by James Croll. Source: Wellcome Collection.

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    before we could be certain whether it was changing its position or not. And even after we had found with certainty that the star was shifting, and this at the rate of 1' in 1800 years, we could not, without a knowledge of its distance, express the angle of displacement in miles. But from the apparent magnitude or brilliancy of the star, we could not determine whether its distance was 10 times, 100 times, or 1000 times that of a Centauri; and consequently we could form no conjec- ture as to the actual velocity of the star. If we assumed its distance to be 10 times that of a Centauri, this would give a transverse velocity of one mile per second. If we assumed its distance to be 100 times that of a Centauri, this would give 10 miles a second as the velocity, and if 1000 times, the velocity of course would be 100 miles per second. As there are but few of the stars which show a measurable parallax, and we have no other reliable method of estimating their distances, ^ it follows that in reference to the greater number of the stars, neither by spectrum-analysis nor by observation of their change of position can we determine their velocities. There does not, therefore, appear to be the shadow of a reason for believing that none of the stars has a motion of over 30 or 40 miles per second : for any thing that at present is known to the contrary, many of them may possess a proper motion enormously greater than that. There is, however, an important point which seems to be overlooked in this objection, viz., that, unless the greater part of the motion of translation be trans- formed into heat, the chances are that no sun star will be formed. It is necessary to the formation of a sun * It is true that we may one day be able to determine by spectrum- analysis the distance of some of the binary stars; but as yet this method has not been applied with success.