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

of the meteorological observations from 1848 to 1868 have been undertaken and completed in the past year. The general state of this work is as follows: The diurnal changes of the dry-bulb thermometer, as depending on the month, on the temperature waves, on the barometric waves, on the overcast and cloudless states of the sky, and on the direction of the wind, have been computed and examined for the whole period; and the exhibition of the results is ready for press. The similar reductions for the wet-bulb thermometer are rapidly approaching completion. --Regarding the preparations for the Transit of Venus Expeditions. Originally five stations were selected and fully equipped with equatoreals, transits, altazimuths, photoheliographs, and clocks; but I have since thought it desirable to supplement these by two branch stations in the Sandwich Islands and one in Kerguelen's Island; and the additional instruments thus required have been borrowed from various sources, so that there is now an abundant supply of instrumental means.... There will thus be available for observation of the Transit of Venus 23 telescopes, nine of which will be provided with double-image-micrometers; and five photoheliographs; and for determination of local time, and latitude and longitude, there will be nine transits and six altazimuths.... All the observers have undergone a course of training in photography; first, under a professional photographer, Mr Reynolds, and subsequently under Capt. Abney, R.E., whose new dry-plate process is to be adopted at all the British Stations.... A Janssen slide, capable of taking 50 photographs of Venus and the neighbouring part of the Sun's limb at intervals of one second, has been made by Mr Dallmeyer for each of the five photoheliographs."--Attached to the Report to the Visitors is a copy of the Instructions to Observers engaged in the Transit of Venus Expeditions, prepared with great care and in remarkable detail.--"In the past spring I published in the Monthly Notices of the Royal Astronomical Society a statement of the fundamental points in a new treatment of the Lunar Theory, by which, availing myself of all that has been done in the best algebraical investigations of that theory, I trust to be able by numerical operations only to give greater accuracy to final results. Considerable progress has been made in the extensive numerical developments, the work being done, at my private expense, entirely by a junior computer; and I hope, at any rate, to put it in such a state that there will be no liability to its entire loss. When this was reported to the Board of Visitors, it was resolved on the motion of Prof. Stokes, that this work, as a public expense, ought to be borne by the Government; and this was forwarded to the Admiralty. On June 24th I wrote to the Secretary of the Admiralty, asking for _L100_ for the present year, which after the usual enquiries and explanations was sanctioned on Aug. 29th."

Of private history: There were short visits to Playford in January, June, and October, but only for a few days in each case.--In March there was a run of two or three days to Newnham (on the Severn) to see the Bore on the Severn, and to Malvern.--In July he went to Newcastle to observe with Mr Newall's great telescope, but the weather was unfavourable: he then went on to Barrow House near Keswick, and spent a few days there, with excursions among the mountains.--On Aug. 13th he went with his daughter Christabel to the Isle of Arran, and then by Glasgow to the Trosachs, where he made several excursions to verify the localities mentioned in the "Lady of the Lake."--While in Scotland he heard of the death of his brother, the Rev. William Airy, and travelled to Keysoe in Bedfordshire to attend the funeral; and returned to Greenwich on Aug. 24th.


1875

"In October of this year I wrote to the Admiralty that I had grounds for asking for an increase of my salary: because the pension which had been settled on my wife, and which I had practically recognized as part of my salary, had been terminated by her death; so that my salary now stood lower by _L200_ than that of the Director of Studies of the Royal Naval College. The Admiralty reply favourably, and on Nov. 27th the Treasury raise my salary to _L1_,200.--For the service of the Clock Movement of the Great Equatoreal, a water-cistern has been established in the highest part of the Ball-Turret, the necessity for which arose from the following circumstance: The Water Clock was supplied by a small pipe, about 80 feet in length, connected with the 3-inch Observatory main (which passes through the Park), at a distance of about 250 feet from any other branch pipe. In spite of this distance I have seen that, on stopping the water-tap in the Battery-Basement under the North-East Turret, the pressure in the gauge of the Water Clock has been instantly increased by more than 40 lbs. per square inch. The consequent derangement of the Water Clock in its now incessant daily use became intolerable. Since the independent supply was provided, its performance has been most satisfactory.--With the Spectroscope the solar prominences have been mapped on 28 days only; but the weather of the past winter was exceptionally unfavourable for this class of observation. After mapping the prominences, as seen on the C line, the other lines, especially F and b, have been regularly examined, whenever practicable. Great care has been taken in determining the position, angle, and heights of the prominences in all cases. The spectrum of Coggia's Comet was examined at every available opportunity last July, and compared directly with that of carbon dioxide, the bands of the two spectra being sensibly coincident. Fifty-four measures of the displacement of lines in the spectra of 10 stars, as compared with the corresponding lines in the spectra of terrestrial elements (chiefly hydrogen), have been made, but some of these appear to be affected by a constant error depending on faulty adjustment of the Spectroscope.--Photographs of the Sun have been taken with the Kew Photoheliograph on 186 days; and of these 377 have been selected for preservation. The Moon, Jupiter, Saturn, and several stars (including the Pleiades and some double stars) have been photographed with the Great Equatoreal, with fairly satisfactory results, though further practice is required in this class of work.--I would mention a supplemental mechanism which I have myself introduced into some chronometers. I have long remarked that, in ordinary good chronometers, the freedom from irregularities depending on mechanical causes is most remarkable; but that, after all the efforts of the most judicious makers, there is in nearly every case a perceptible defect of thermal compensation. There is great difficulty in correcting the residual fault, not only because an inconceivably small movement of the weights on the balance-curve is required, but also because it endangers the equilibrium of the balance. The mechanism adopted to remedy the defect is described in a Paper in the Horological Journal of July 1875 by Mr W. Ellis, and has received the approval of some able chronometer-makers.--With respect to the Transit of Venus Expeditions: The parties from Egypt and Rodriguez are returned. I am in continual expectation of the arrival of the other parties. I believe the eye-observations and the ordinary photographs to be quite successful; I doubt the advantage of the Janssen; one of the double-image-micrometers seems to have failed; and the Zenith-telescope gives some trouble. At three stations at Rodriguez, and three at Kerguelen, the observations appear to have been most successful. At the Sandwich Islands, two of the stations appear to have been perfectly successful (except that I fear that the Janssen has failed), and a rich series of lunar observations for longitude is obtained. At New Zealand, I grieve to say, the observations were totally lost, entirely in consequence of bad weather. There has been little annoyance from the dreaded 'black drop.' Greater inconvenience and doubt have been caused by the unexpected luminous ring round Venus.--With regard to the progress of my proposed New Lunar Theory: Three computers are now steadily employed on the work. It will be remembered that the detail and mass of this work are purely numerical; every numerical coefficient being accompanied with a symbolical correction whose value will sometimes depend on the time, but in every case is ultimately to be obtained in a numerical form. Of these coefficients, extracted (for convenience) from Delaunay's results, there are 100 for parallax, 182 for longitude, 142 for latitude; the arguments being preserved in the usual form."--After reviewing the changes that had taken place at the Observatory during the past forty years, the Report to the Board of Visitors concludes thus: "I much desire to see the system of time-signals extended, by clocks or daily signals, to various parts of our great cities and our dockyards, and above all by hourly signals on the Start Point, which I believe would be the greatest of all benefits to nautical chronometry. Should any extension of our scientific work ever be contemplated, I would remark that the Observatory is not the place for new physical investigations. It is well adapted for following out any which, originating with private investigators, have been reduced to laws susceptible of verification by daily observation. The National Observatory will, I trust, always remain on the site where it was first planted, and which early acquired the name of 'Flamsteed Hill.' There are some inconveniences in the position, arising principally from the limited extent of the hill, but they are, in my opinion, very far overbalanced by its advantages."--In a letter on the subject of the Smith's Prizes Examination at Cambridge, which was always a matter of the greatest interest to him, Airy renewed his objections to the preponderance in the Papers of a class of Pure Mathematics, which he considered was never likely under any circumstances to give the slightest assistance to Physics. And, as before, these remarks called forth a rejoinder from Prof. Cayley, who was responsible for many of the questions of the class referred to.--In this year Airy completed his "Notes on the Earlier Hebrew Scriptures," which were shortly afterwards published as a book by Messrs Longmans, Green, & Co. In his letter to the publishers introducing the subject, he says, "For many years past I have at times put together a few sentences explanatory as I conceive of the geographical and historical circumstances connected with the principal events recorded in the Hebrew Scriptures. The view which I take is free, but I trust not irreverent. They terminate with a brief review of Colenso's great work. The collection now amounts to a small book." From the references already given in previous years to his Papers and correspondence on the geography of Exodus, his correspondence with Colenso, &c. &c., it will be seen that he took a great interest in the early history of the Israelites.--On August 10th, 1875, Airy celebrated the Bicentenary of the Royal Observatory by a dinner in the Octagon Room, which was attended by the Presidents of the Royal Society and the R. Astr. Society, and by a large number of Scientific gentlemen interested in Astronomy.--In February he was revising his Treatise on "Probabilities."

Of private history: up to Jan. 16th Airy was at Playford as usual.--For about a week in April he was in the Isle of Man with his daughter Christabel.--In June there was a short trip to Salisbury, Blandford, and Wimborne.--On August 12th he started with his daughter Annot for a holiday in Cumberland, but on the next day he was recalled by a telegram with the intelligence that a change for the worse had come over his wife's health. Lady Airy died on August 13th, 1875. For the last