Autobiography of Sir George Biddell Airy - George Biddell Airy (android based ebook reader txt) 📗

field of view of the Transit Circle. The reflector was cleaned, but in vain; at last it was discovered that one of the lenses (the convex lens) of the combination which forms the object-glass of a Reversed Telescope in the interior of the Transit-axis, and through which all illuminating light must pass, had become so corroded as to be almost opaque.'--The South-East Equatoreal has been partly occupied with the thermo-multiplier employed by Mr Stone for the measure of heat radiating from the principal stars. Mr Stone's results for the radiation from Arcturus and alpha Lyrae appear to be incontrovertible, and to give bases for distinct numerical estimation of the radiant heat of these stars.--In my last Report I alluded to a proposed systematic reduction of the meteorological observations during the whole time of their efficient self-registration. Having received from the Admiralty the funds necessary for immediate operations, I have commenced with the photographic registers of the thermometers, dry-bulb and wet-bulb, from 1848 to 1868.--Our chronometer-room contains at present 219 chronometers, including 37 chronometers which have been placed here by chronometer-makers as competing for the honorary reputation and the pecuniary advantages to be derived from success in the half-year's trial to which they are subjected. I take this opportunity of stating that I have uniformly advocated the policy of offering good prices for the chronometers of great excellence, and that I have given much attention to the decision on their merits; and I am convinced that this system has greatly contributed to the remarkably steady improvement in the performance of chronometers. In the trial which terminated in August 1869, the best chronometers (taking as usual the average of the first six) were superior in merit to those of any preceding year.--With the funds placed at my disposal for the Transit of Venus 1874 I purchased three 6-inch equatoreals, and have ordered two: I have also ordered altazimuths (with accurate vertical circles only), and clocks sufficient, as I expect, to equip five stations. For methods of observation, I rely generally on the simple eye-observation, possibly relieved of some of its uncertainty by the use of my colour-correcting eyepiece. But active discussion has taken place on the feasibility of using photographic and spectroscopic methods; and it will not be easy for some time to announce that the plan of observations is settled.--There can be no doubt, I imagine, that the first and necessary duty of the Royal Observatory is to maintain its place well as an Observing Establishment; and that this must be secured, at whatever sacrifice, if necessary, of other pursuits. Still the question has not unfrequently presented itself to me, whether the duties to which I allude have not, by force of circumstances, become too exclusive; and whether the cause of Science might not gain if, as in the Imperial Observatory of Paris for instance, the higher branches of mathematical physics should not take their place by the side of Observatory routine. I have often felt the desire practically to refresh my acquaintance with what were once favourite subjects: Lunar Theory and Physical Optics. But I do not at present clearly see how I can enter upon them with that degree of freedom of thought which is necessary for success in abstruse investigations."

Of private history: There was a longer visit than usual to Playford, lasting till Jan. 27th.--In April he made a short excursion (of less than a week) with his son Hubert to Monmouth, &c.--From June 14th to July 2nd he was staying at Barrow House, near Keswick, with his son Hubert: during this time he was much troubled with a painful skin-irritation of his leg and back, which lasted in some degree for a long time afterwards.--From Sept. 25th to Oct. 6th he made an excursion with his daughter Christabel to Scarborough, Whitby, &c., and again spent a few days at Barrow House.


1871

"In April 1870 the Assistants had applied for an increase of salary, a request which I had urged strongly upon the Admiralty. On Jan. 27 of this year the Admiralty answered that, on account of Mr Childers's illness, the consideration must be deferred to next year! The Assistants wrote bitterly to me: and with my sanction they wrote to the First Lord. On Jan. 31st I requested an interview with Mr Baxter (secretary of the Admiralty), and saw him on Feb. 3rd, when I obtained his consent to an addition of _L530_. There was still a difficulty with the Treasury, but on June 27th the liberal scale was allowed.--Experiments made by Mr Stone shew clearly that a local elevation, like that of the Royal Observatory on the hill of Greenwich Park, has no tendency to diminish the effect of railway tremors.--The correction for level error in the Transit Circle having become inconveniently large, a sheet of very thin paper, 1/270 inch in thickness, was placed under the eastern Y, which was raised from its bed for the purpose. The mean annual value of the level-error appears to be now sensibly zero.--As the siege and war operations in Paris seriously interfered with the observations of small planets made at the Paris Observatory, observations of them were continued at Greenwich throughout each entire lunation during the investment of the city.--The new Water-Telescope has been got into working order, and performs most satisfactorily. Observations of gamma Draconis have been made with it, when the star passed between 20h and 17h, with some observations for adjustment at a still more advanced time. As the astronomical latitude of the place of observation is not known, the bearing of these observations on the question of aberration cannot be certainly pronounced until the autumn observations shall have been made; but supposing the geodetic latitude to be accordant with the astronomical latitude, the result for aberration appears to be sensibly the same as with ordinary telescopes.--Several years since, I prepared a barometer, by which the barometric fluctuations were enlarged, for the information of the public; its indications are exhibited on the wall, near to the entrance gate of the Observatory. A card is now also exhibited, in a glass case near the public barometer, giving the highest and lowest readings of the thermometer in the preceding twenty-four hours.--Those who have given attention to the history of Terrestrial Magnetism are aware that Halley's Magnetic Chart is very frequently cited; but I could not learn that any person, at least in modern times, had seen it. At last I discovered a copy in the library of the British Museum, and have been allowed to take copies by photolithography. These are appended to the Magnetical and Meteorological Volume for 1869.--The trials and certificates of hand-telescopes for the use of the Royal Navy have lately been so frequent that they almost become a regular part of the work of the Observatory. I may state here that by availing myself of a theory of eyepieces which I published long since in the Cambridge Transactions, I have been able to effect a considerable improvement in the telescopes furnished to the Admiralty.--The occurrence of the Total Eclipse of the Sun in December last has brought much labour upon the Observatory. As regards the assistants and computers, the actual observation on a complicated plan with the Great Equatoreal (a plan for which few equatoreals are sufficiently steady, but which when properly carried out gives a most complete solution of the geometrical problem) has required, in observation and in computation, a large expenditure of time.--My preparations for the Transit of Venus have respect only to eye-observation of contact of limbs. With all the liabilities and defects to which it is subject, this method possesses the inestimable advantage of placing no reliance on instrumental scales. I hope that the error of observation may not exceed four seconds of time, corresponding to about 0.13" of arc. I shall be very glad to see, in a detailed form, a plan for making the proper measures by heliometric or photographic apparatus; and should take great interest in combining these with the eye-observations, if my selected stations can be made available. But my present impression is one of doubt on the certainty of equality of parts in the scale employed. An error depending on this cause could not be diminished by any repetition of observations."--After referring to the desirability of vigorously prosecuting the Meteorological Reductions (already begun) and of discussing the Magnetic Observations, the Report concludes thus: "There is another consideration which very often presents itself to my mind; the waste of labour in the repetition of observations at different observatories..... I think that this consideration ought not to be put out of sight in planning the courses of different Observatories."--In this year De Launay's Lunar Theory was published. This valuable work was of great service to Airy in the preparation of the Numerical Lunar Theory, which he subsequently undertook.--In the latter part of this year Airy was elected President of the Royal Society, and held the office during 1872 and 1873. At this time he was much pressed with work, and could ill afford to take up additional duties, as the following quotation from a letter to one of his friends shews: "The election to the Presidency of R.S. is flattering, and has brought to me the friendly remembrances of many persons; but in its material and laborious connections, I could well have dispensed with it, and should have done so but for the respectful way in which it was pressed on me."

Of private history: There was the usual winter visit to Playford.--In April he made a short trip to Cornwall with his daughter Annot.--In June he was appointed a Companion of the Bath, and was presented at Court on his appointment.--Mrs Airy was staying with her daughter, Mrs Routh, at Hunstanton, during June, her state of health being somewhat improved.--From August 1st to 28th he was chiefly in Cumberland, at Barrow House, and at Grange, Borrowdale, where his son Osmund was staying for a holiday.


1872

"From the Report to the Board of Visitors it appears that 'The Normal Siderial Clock for giving sidereal time by galvanic communication to the Astronomical Observatory was established in the Magnetic Basement in 1871, June; that locality being adapted for it on account of the uniformity of temperature, the daily changed of temperature rarely exceeding 1 deg. Fahrenheit. Its escapement is one which I suggested many years ago in the Cambridge Transactions; a detached escapement, very closely analogous to the ordinary chronometer escapement, the pendulum receiving an impulse only at alternate vibrations.... The steadiness of rate is very far superior to any that we have previously attained.'--The aspect of railway enterprise is at present favourable to the Park and to the Observatory. The South-Eastern Railway Company has made an arrangement with the Metropolitan Board of Works for shifting the course of the great Southern Outfall Sewer. This enables the Company to trace a new line for the railway, passing on the north side of London Street, at such a distance from the Observatory as to remove all cause of alarm. I understand that the Bill, which was unopposed, has passed the Committee of the House of Commons. I trust that the contest, which has lasted thirty-seven years, is now terminated.--The observations of 7 Draconis with the Water-Telescope, made in the autumn of 1871, and the spring of 1872, are reduced, the latter only in their first steps.... Using the values of the level scales as determined by Mr Simms (which I have no reason to believe to be inaccurate) the spring and autumn