Autobiography of Sir George Biddell Airy, George Biddell Airy [best english books to read for beginners txt] 📗

to make observations on Earth-disturbance by railways there. I had been before the Committee on May 25th. On Sept. 1st I approved of an amended plan. In reference to this matter the Report states that 'It is proper to remark that the shake of the Altazimuth felt in the earthquake of 1863, Oct. 5th, when no such shake was felt with instruments nearer to the ground (an experience which, as I have heard on private authority, is supported by observation of artificial tremors), gives reason to fear that, at distances from a railway which would sufficiently defend the lower instruments, the loftier instruments (as the Altazimuth and the Equatoreals) would be sensibly affected.'--Some of the Magnets had been suspended by steel wires, instead of silk, of no greater strength than was necessary for safety, and the Report states that 'Under the pressure of business, the determination of various constants of adjustment was deferred to the end of the year. The immediate results of observation, however, began to excite suspicion; and after a time it was found that, in spite of the length of the suspending wire (about 8 feet) the torsion-coefficient was not much less than 1/6. The wires were promptly dismounted, and silk skeins substituted for them. With these, the torsion-coefficient is about 1/210.'--The Dip-Instrument, which had given great trouble by the irregularities of the dip-results, had been compared with two dip-instruments from Kew Observatory, which gave very good and accordant results. 'It happened that Mr Simms, by whom our instruments now in use were prepared, and who had personally witnessed our former difficulties, was present during some of these experiments. Our own instrument being placed in his hands (Nov. 10th to 19th) for another purpose, he spontaneously re-polished the apparently faultless agate-bearings. To my great astonishment, the inconsistencies of every kind have nearly or entirely vanished. On raising and lowering the needles, they return to the same readings, and the dips with the same needle appear generally consistent.' Some practical details of the polishing process by which this result had been secured are then given.--After numerous delays, the apparatus for the self-registration of Spontaneous Earth Currents was brought into a working state in the month of March. A description of the arrangement adopted is given in the Report.--'All Chronometers on trial are rated every day, by comparison with one of the clocks sympathetic with the Motor Clock. Every Chronometer, whether on trial or returned from a chronometer-maker as repaired, is tried at least once in the heat of the Chronometer-Oven, the temperature being usually limited to 90 deg. Fahrenheit; and, guided by the results of very long experience, we have established it as a rule, that every trial in heat be continued through three weeks.'--'The only employment extraneous to the Observatory which has occupied any of my time within the last year is the giving three Lectures on the Magnetism of Iron Ships (at the request of the Lords of the Committee of Council on Education) in the Theatre of the South Kensington Museum. The preparations, however, for these Lectures, to be given in a room ill-adapted to them, occupied a great deal of my own time, and of the time of an Assistant of the Observatory.'--'Referring to a matter in which the interests of Astronomy are deeply concerned, I think it right to report to the Visitors my late representation to the Government, to the effect that, in reference to possible observation of the Transit of Venus in 1882, it will be necessary in no long time to examine the coasts of the Great Southern Continent.'"

Of private history: "There were the usual visits to Playford at the beginning and end of the year.--From June 18th to 26th I was on a trip in Wales with my sons Hubert and Osmund.--From Sept. 6th to Oct. 2nd I was staying with most of my family at Portinscale near Keswick: we returned by Barnard Castle, Rokeby, &c."


CHAPTER VIII.

AT GREENWICH OBSERVATORY--1866 TO 1876.


1866

In this year the cube of the Transit Circle was pierced, to permit reciprocal observations of the Collimators without raising the instrument. This involved the construction of improved Collimators, which formed the subject of a special Address to the Members of the Board of Visitors on Oct. 21st 1865.--From the Report to the Visitors it appears that "On May 23rd 1865, a thunderstorm of great violence passed very close to the Observatory. After one flash of lightning, I was convinced that the principal building was struck. Several galvanometers in the Magnetic Basement were destroyed. Lately it has been remarked that one of the old chimneys of the principal building had been dislocated and slightly twisted, at a place where it was surrounded by an iron stay-band led from the Telegraph Pole which was planted upon the leads of the Octagon Room."--"On consideration of the serious interruptions to which we have several times been exposed from the destruction of our open-air Park-wires (through snow-storms and gales), I have made an arrangement for leading the whole of our wires in underground pipes as far as the Greenwich Railway Station."--"The Committee of the House of Commons, to whom the Greenwich and Woolwich Line of the South Eastern Railway was referred, finally assented to the adoption of a line which I indicated, passing between the buildings of the Hospital Schools and the public road to Woolwich."--"The Galvanic Chronometer attached to the S. E. Equatoreal often gave us a great deal of trouble. At last I determined, on the proposal of Mr Ellis, to attempt an extension of Mr R. L. Jones's regulating principle. It is well known that Mr Jones has with great success introduced the system of applying galvanic currents originating in the vibrations of a normal pendulum, not to drive the wheelwork of other clocks, but to regulate to exact agreement the rates of their pendulums which were, independently, nearly in agreement; each clock being driven by weight-power as before. The same principle is now applied to the chronometer.... The construction is perfectly successful; the chronometer remains in coincidence with the Transit Clock through any length of time, with a small constant error as is required by mechanical theory."--"The printed volume of Observations for 1864 has two Appendixes; one containing the calculations of the value of the Moon's Semi-diameter deduced from 295 Occultations observed at Cambridge and Greenwich from 1832 to 1860, and shewing that the Occultation Semi-diameter is less than the Telescopic Semi-diameter by 2"; the other containing the reduction of the Planetary Observations made at the Royal Observatory in the years 1831-1835; filling up the gap, between the Planetary Reductions 1750-1830 made several years ago under my superintendence, and the Reductions contained in the Greenwich Volumes 1836 to the present time: and conducted on the same general principles."--"Some trouble had been found in regulating the temperature of the Magnetic Basement, but it was anticipated that in future there would be no difficulty in keeping down the annual variation within about 5 deg. and the diurnal variation within 3 deg..--Longitudes in America were determined in this year by way of Valencia and Newfoundland: finished by Nov. 14th."

Of private history: In April he made a short visit to Ventnor in the Isle of Wight.--From June 15th to July 23rd he was on an expedition in Norway with his son Osmund and his nephew Gorell Barnes.--There was probably a short stay at Playford in the winter.

In this and in the previous year (1865) the free-thinking investigations of Colenso, the Bishop of Natal, had attracted much notice, and had procured him the virulent hostility of a numerous section. His income was withheld from him, and in consequence a subscription fund was raised for his support by his admirers. Airy, who always took the liberal side in such questions, was a subscriber to the fund, and wrote the following letter to the Bishop:

ROYAL OBSERVATORY, GREENWICH, S.E.,
1865, July 24 .

MY LORD,

With many thanks I have to acknowledge your kind recollection of me in sending as a presentation copy the work on Joshua, Judges, and especially on the divided authorship of Genesis; a work whose investigations, founded in great measure on severe and extensive verbal criticism, will apparently bear comparison with your Lordship's most remarkable examination of Deuteronomy. I should however not do justice to my own appreciation if I did not remark that there are other points considered which have long been matters of interest to me.

On several matters, some of them important, my present conclusions do not absolutely agree with your Lordship's. But I am not the less grateful for the amount of erudition and thought carefully directed to definite points, and above all for the noble example of unwearied research and freedom in stating its consequences, in reference to subjects which scarcely ever occupy the attention of the clergy in our country.

I am, My Lord,
Yours very faithfully,
G.B. AIRY.

The Lord Bishop of Natal .

* * * * *

Here also is a letter on the same subject, written to Professor Selwyn, Professor of Divinity at Cambridge:--


ROYAL OBSERVATORY, GREENWICH,
LONDON, S.E.,
1866, May 5 .

MY DEAR SIR,

The MS. concerning Colenso duly arrived.

I note your remarks on the merits of Colenso. I do not write to tell you that I differ from you, but to tell you why I differ.

I think that you do not make the proper distinction between a person who invents or introduces a tool, and the person who uses it.

The most resolute antigravitationist that ever lived might yet acknowledge his debt to Newton