Address / of George Gabriel Stokes.

  • Sir George Stokes, 1st Baronet
Date:
[1869?]
Catalogue details

Licence: Public Domain Mark

Credit: Address / of George Gabriel Stokes. Source: Wellcome Collection.

    8/20 (page 8)
    tween the solar F and that of Sirius is due to proper motion, Mr. Huggins concludes from his measures of the minute difference of position that at the time of the observation Sirius was receding from the earth at the rate of 41-4 miles per second. A part of this was due to the motion of the earth in its orbit; and on deducting the orbital velocity of the earth, resolved in the direc¬ tion of a line drawn from the star, there remained 29-4 miles per second as the velocity with which Sirius and our sun are mutually receding from each other. Considering the minuteness of the quantity on which the result de¬ pends, it is satisfactory to find that Mr. Huggins’s results as to the motion of Sirius have been confirmed by the observations of Father Secchi made at Home with a different instrument. The determination of radial proper motion in this way is still in its infancy. It is worthy of note that, unlike the detection of transversal proper motion by change of angular position, it is equally applicable to stars at all distances, provided they are bright enough to render the observations possible. It is conceivable that the results of these observations may one day lead to a de¬ termination of the motion of the solar system in space, which is more trust¬ worthy than that which has been deduced from changes of position, as being founded on a broader induction, and not confined to conclusions derived from the stars in our neighbourhood. Should even the solar system and the nearer stars be drifting along, as Sir John Herschel suggests, with an approximately common motion, like motes in a sunbeam, it is conceivable that the circum¬ stance might thus be capable of detection. To what wide speculations are we led as to the possible progress of our knowledge when we put together what has been accomplished in different branches of science ! I turn now to another recent application of spectral analysis. The pheno¬ menon of a total solar eclipse is described by those who have seen it as one of the most imposing that can be witnessed. The rarity of its occurrence and the shortness of its duration afford, however, opportunity for only a hasty study of the phenomena which may then present themselves. Among these, one of the most remarkable, seen indeed before, but first brought prominently into notice by the observers who watched the eclipse of July 7, 1842, consists in a series of mountain-like or cloud-like luminous objects seen outside the dark disk of the moon. These have been seen in subsequent total eclipses, and more specially studied, by means of photography, by Mr. Warren De La Hue in the eclipse of June 18, 1860. The result of the various observations, and especially the study, which could be made at leisure, of the photographs obtained by Mr. De La Kue, proved conclusively that these appendages belong to the sun, not to the moon. The photographs proved further their light to be remarkable for actinic power. Since that time the method of spectral analysis has been elaborated ; and it seemed likely that additional informa¬ tion bearing on the nature of these objects might be obtained by the applica¬ tion of the spectroscope. Accordingly various expeditions were equipped for the purpose of observing the total solar eclipse which was to happen on