Of printed papers by Airy in this year the most important was one on the “Results deduced from the Measures of Terrestrial Magnetic Force in the Horizontal Plane,” &c.  This was a long Paper, communicated to the Royal Society, and published in the Phil.  Trans., and was the last Scientific Paper of any importance (except the Volume of the Numerical Lunar Theory) in the long list of “Papers by G.B.  Airy.”  The preparation of this Paper took much time.—­Of miscellaneous matters:  In May a Committee of the Royal Society had been appointed to advise the India Office as to the publication of Col.  J. Herschel’s pendulum observations in India; and Airy was asked to assist the Committee with his advice.  He gave very careful and anxious consideration to the subject, and it occupied much time.—­In the early part of the year he was asked by Sir William Thomson to assist him with an affidavit in a lawsuit concerning an alleged infringement of one of his Patents for the improvement of the Compass.  Airy declined to make an affidavit or to take sides in the dispute, but he wrote a letter from which the following is extracted:  “I cannot have the least difficulty in expressing my opinion that you have made a great advance in the application of my method of correcting the compass in iron ships, by your introduction of the use of short needles for the compass-cards.  In my original investigations, when the whole subject was in darkness, I could only use existing means for experiment, namely the long-needle compasses then existing.  But when I applied mechanical theory to explanation of the results, I felt grievously the deficiency of a theory and the construction which it suggested (necessarily founded on assumption that the proportion of the needle-length to the other elements of measure is small) when the length of the needles was really so great.  I should possibly have used some construction like yours, but the Government had not then a single iron vessel, and did not seem disposed to urge the enquiry.  You, under happier auspices, have successfully carried it out, and, I fully believe, with much advantage to the science.”—­He wrote a Paper for the Athenaeum and had various correspondence on the subject of the Badbury Rings in Dorsetshire, which he (and others) considered as identical with the “Mons Badonicus” of Gildas, the site of an ancient British battle.—­In February he was in correspondence with the Astronomer Royal on Uniform Time Reckoning, and on considerations relating to it.—­On June 6th he attended the Annual Visitation of the Observatory, and brought before the Board his investigations of the Diurnal Magnetic Inequalities, and the revises of his Lunar Theory.

1886