196 HISTORY OF THE [1870-80 The preparations for the expedition were attended by an incident almost tragic. At the meeting in May, Lord Lindsay exhibited this heliometer that he had put at the disposal of Mr. Gill for the observations of the coming opposition of Mars, and in preparation for the exhibition the instrument was set up in the meeting-room at Burlington House a few days previously, with the polar axis in the position relative to the horizon that it would have at Ascension, latitude 8 S. In making a final necessary alteration a holding screw was turned which proved to be shorter than was to be expected and had run out ; so there was nothing to keep down the lower end of the polar axis, and this with all it carried crashed to the ground. The instrument alighted on the eye-end, which was driven through the floor and snapped off, and by this means the shock of the fall was broken and less damage was done than might have been expected. After the meeting the heliometer tube was sent to Messrs. Troughton & Simms, while Messrs. Cooke & Sons and Mr. John Browning repaired the mount- ing. Within ten days all was again in order, the instrument tested, packed and stowed on board ship. Short reports from Mr. Gill during his stay at Ascension will be found at various places in the Monthly Notices,* and the definite results in volume 46 of the Memoirs. Mrs. Gill's book, Six Months in Ascension, An Unscien- tific Account of a Scientific Expedition, tells the story from another point of view. Mr. and Mrs. Gill returned to England in 1878 January. The solar parallax was a prominent feature of the session 1877-78. Sir George Airy opened the meeting in 1877 November by announcing the value of the constant 8 "-760 derived from the British observations of the Transit of Venus and published in the Parliamentary Report. Mr. Stone sent from the Cape a re-dis- cussion of the same observations, interpreting the meaning of the word " contact " according to his own view, which was different to that adopted in the official reduction, and derived the considerably different value 8 "-884. This was received at the meeting in March and led to some discussion, Mr. Gill objecting to so large a value on the ground that it was not consistent with Struve's constant of aberration and Cornu's value of the velocity of light. A second paper by Mr. Stone, to be found in the Monthly Notices for April, in which he discussed the observations of contact made at the Cape, apparently because he felt they had not been given sufficient weight, in the official reduction, two of them having been rejected, supported his previous result and led him to affirm that the value of the solar parallax must lie between 8"-84 and 8"-g2. At the meeting in June, Captain Tupman, under
- Vol. 37, 310-326; 38, i-n, 17-21, 57-58, 89-90.
