pulse

The "Pulse" is 32.955 Earth days. It was first discovered by the Solar Physicist Balfour Stewart as a short term sunspot cycle, and published in The Report of The 51st Meeting of The British Association For The Advancement of Science, held at York in 1881 in a paper entitled "On the Possibility of the Existence of Intra-Mercurial Planets, by Balfour Stewart, LL.D., F.R.S. (in The Transactions of Section A. Pages 518 to 519). Below you can see a complete set of scans of this paper, with the salient details magnified for easy reading.