In a paper published in vol. xli., part i., of the Transactions of this Society, entitled “Spectroscopic Observations of the Rotation of the Sun,” I communicated the first results obtained with a spectroscope specially designed for the purpose of measuring the displacements of the solar lines on opposite limbs of the sun occasioned by the motions of the absorbing gases to or from the observer in consequence of the sun's axial rotation. The investigation was originally undertaken with the view of ascertaining whether the peculiar law of surface rotation of the sun, first discovered by Carrington from the motions of solar spots, and afterwards confirmed by Dunér from spectroscopic observations similar to my own, was, or was not, subject to alterations depending on the general state of solar activity.