“My lectures in this term were to the Junior Sophs from Apr. 10th to May 13th:  they were six in number and not very regular.  On Apr. 28th I sent to Mawman the copy of my Trigonometry for the Encyclopaedia Metropolitana, for which I received L42.  I received notice from the Press Syndicate that the price of my Mathematical Tracts was fixed at 6s. 6d.:  I sold the edition to Deighton for L70, and it was immediately published.  About this time I have letters from Mr Herschel and Sir H. Davy about a Paper to be presented to the Royal Society—­I suppose about the Figure of the Earth to the 2nd order of ellipticity, which was read to the Royal Society on June 15th.

“On Saturday, May 13th, 1826, I went to London on the way to Dolcoath, and received four chronometers from the Royal Observatory, Greenwich.  I travelled by Devonport and Falmouth to Camborne, where I arrived on May 20th and dined at the count-house dinner at the mine.  I was accompanied by Ibbotson, who was engaged as a pupil, and intended for an engineer.  On May 24th Whewell arrived, and we took a pendulum and clock down, and on the 30th commenced the observation of coincidences in earnest.  This work, with the changing of the pendulums, and sundry short expeditions, occupied nearly three weeks.  We had continued the computation of our observations at every possible interval.  It is to be understood that we had one detached pendulum swinging in front of a clock pendulum above, and another similarly mounted below; and that the clocks were compared by chronometers compared above, carried down and compared, compared before leaving, and brought up and compared.  The upper and lower pendulums had been interchanged.  It was found now that the reliance on the steadiness of the chronometers was too great; and a new method was devised, in which for each series the chronometers should make four journeys and have four comparisons above and two below.  This arrangement commenced on the 19th June and continued till the 20th.  On the 26th we packed the lower instruments, intending to compare the pendulum directly with the upper one, and sent them up the shaft:  when an inexplicable occurrence stopped all proceedings.  The basket containing all the important instruments was brought up to the surface (in my presence) on fire; some of the instruments had fallen out with their cases burning.  Whether a superstitious miner had intentionally fired it, or whether the snuff of a candle had been thrown into it, is not known.  Our labour was now rendered useless.  On the 28th I packed up what remained of instruments, left for Truro, and arrived at Bury on July 1st.  During our stay in Cornwall I had attended a ‘ticketing’ or sale of ore at Camborne, and we had made expeditions to the N.W.  Coast, to Portreath and Illogan, to Marazion and St Michael’s Mount, and to Penzance and the Land’s End.  On July 3rd I saw Mr Cropley in Bury gaol, and went to Cambridge.  On the 4th I was admitted A.M., and on the 5th was admitted Major Fellow.