Page:Proceedings of the Royal Society of London Vol 69.djvu/229

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From the top of a small hillock within two minutes' walk of the instruments we could see the camp of the Boston expedition near Sawah Loento, at a distance of 2·7 miles (measured on the Survey maps 1:20,000). Professors Burton and Hosmer were so kind as to make an arrangement by which we received time signals and so determined the errors and rates of the chronometer and watch which I had brought with me. Professor Hosmer had a white time-ball fixed that could easily be seen against the dark background of the tropical foliage with the help of binoculars; and it was arranged that on any day that we hung out a signal (three white flags) in the early morning, he would if possible drop the time-ball at 11h 5m 0s, again at 11h 6m 0s and at 11h 7m 0s. His time observations for determining the errors and rates of his own chronometers were made with a 2-½ inch portable transit and chronograph. Mr. Hosmer gave me signals on four days between the 9th and 19th of May. My watch—an excellent one by Frodsham, made for the 1862 Exhibition—was kept in exceptionally favourable conditions for good time-keeping, and its rate deduced from signals received on May 9 and 16 was + 4·6 seconds per diem, and from May 16 and 19 was + 4·6 seconds per diem.

The rate of the chronometer (by Crisp) was found to have changed from + 0s·7 between the 17th and 18th to + 2s·1 between 18th and 19th, the chronometer having been moved in and out of the hut several times for the preparatory rehearsals.

The following are the times of contacts observed, those predicted from the elements given in the 'Nautical Almanac' being given for comparison and position-angles of the contacts being also added for convenience of record:—

First contact was observed by me through the declination theodolite, the time of my call "Now" (possibly 5 seconds late) being noted on the Crisp chronometer by Lieutenant Briggs. Second and third contacts are those for Dr. Wallace's signal "Go" at beginning of totality when he was observing the disappearing current on the focussing plate of the Dallmeyer telephotographic camera (image of sun 1·43 inches in diameter) and for my signal "Now" given to Lieutenant