The spectroscope and its work / [Richard A. Proctor].

  • Proctor, Richard A. (Richard Anthony), 1837-1888.
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: The spectroscope and its work / [Richard A. Proctor]. Source: Wellcome Collection.

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    next is shown the broad F line in the spectrum of Sirius, displaced towards the red. Next is the F line in the solar spectrum. Below that again is the spectrum of hydrogen at atmospheric pressure. It is important to notice these two lower spectra. They indicate what had been observed by Huggins, in confirmation of observations previously made by Pliicker and Hittorf, respecting the widening of this line of hydrogen under increase of pressure, viz., that the line widens symmetrically on either side of its position as a thin line. Hence the displacement of the F line of Sirius can be explained only by the motion of Sirius; and as the displacement is towards the red, the star is receding from the earth. The amount of the observed dis- placement indicated a motion of recession at the rate of about forty-one and a half miles per second. But as the earth had at the time a motion of recession from Sirius, due to her own motion in her orbit, at the rate of about twelve miles per second, there remained a balance of almost twenty-nine and a half miles of recessional motion per second. The sun himself is in motion towards the constellation Hercules, though his rate of motion is uncertain. I place no reliance myself on Otto Struve’s estimate of the rate of this motion, having been able to show that the assumptions on which his reasoning is based are not sound. According to his estimate the sun’s motion from Sirius would be rather more than three miles per second, leaving about twenty- six miles per second for the actual recession of Sirius from the part of space through which we are travelling. I believe that a much larger proportion of the relative recessional motion of Sirius is due to our sun’s motion. Be this as it may, however, there can be no doubt that the distance between Sirius and the sun is increasing at the rate of nearly thirty miles per second; for Huggins’s result has since been confirmed by himself with better instrumental means, and also by Mr. Christie at the Greenwich Observatory. Subsequent observations by Mr. Huggins have h 2