The critical trial depends on the great mass of computations in Section II.  These have been made in duplicate, with all the care for accuracy that anxiety could supply.  Still I cannot but fear that the error which is the source of discordance must be on my part.  I cannot conjecture whether I may be able to examine sufficiently into this matter.”  He resolutely took in hand the revision of his work, and continued it till October 1888.  But it is clear from the entries in his journal that his powers were now unequal to the task, and although from time to time he suspected that he had discovered errors, yet it does not appear that he determined anything with certainty.  He never doubted that there were important errors in the work, and later on he left the following private note on the subject: 

NUMERICAL LUNAR THEORY.

1890, Sept. 29.

I had made considerable advance (under official difficulties) in calculations on my favourite Numerical Lunar Theory, when I discovered that, under the heavy pressure of unusual matters (two Transits of Venus and some eclipses) I had committed a grievous error in the first stage of giving numerical value to my Theory.

My spirit in the work was broken, and I have never heartily proceeded with it since.

G.B.  AIRY.

Probably the error referred to here is the suspected error mentioned above in his Report of 1878, as to which he subsequently became more certain.

Whatever may be the imperfections of the Numerical Lunar Theory, it is a wonderful work to have been turned out by a man 85 years old.  In its idea and inception it embodies the experience of a long life actively spent in practical science.  And it may be that it will yet fulfil the objects of its author, and that some younger astronomer may take it up, correct its errors (wherever they may be), and fit it for practical use.  And then the labour bestowed upon it will not have been in vain.

Subject always to the absorbing occupations of the Lunar Theory he amused himself with reading his favourite subjects of History and Antiquities.  His movements during the remainder of the year 1881 were as follows:  In September he paid a two days’ visit to Lady Herschel at Hawkhurst.  From Oct. 4th to 17th he was at the Cumberland Lakes and engaged in expeditions in the neighbourhood.  From Nov. 5th to 8th he was at Cambridge, inspecting Prof.  Stuart’s workshops, and other scientific institutions.  On Dec. 13th he went to Playford.—­Amongst miscellaneous matters:  in November he wrote to Mr Rothery on the loss of the ‘Teuton’ at some length, with suggestions for the safer construction of such vessels.—­In October he was asked for suggestions regarding the establishment of a “Standard Time” applicable to the railway traffic in the United States:  he replied as follows: 

1881, Oct. 31.

SIR,