Circ.u.mstances have enabled me lately to obtain private information of a most accurate kind on the late Mathematical Tripos: and among other things, I have received a statement of every individual question answered or partly answered by five honour-men. I have collected the numbers of these in a small table which I enclose.

I am struck with the _almost_ nugatory character of the five days'

honour examination as applied to Senior Optimes, and I do not doubt that it is _totally_ nugatory as applied to Junior Optimes. It appears to me that, for all that depends on these days, the rank of the Optimes is mere matter of chance.

In the examinations of the Civil Service, the whole number of marks is published, and also the number of marks gained by each candidate. I have none of their papers at hand, but my impression is that the lowest candidates make about 1 in 3; and the fair candidates about 2 in 3, instead of 1 in 10 or 1 in 13 as our good Senior Optimes.

I am, my dear Master, Very truly yours, G.B. AIRY.

_The Rev. Dr Cookson, Master of St Peters College, &c. &c._

The Table referred to in the above letter is as follows:

Number of Questions, and numbers of Answers to Questions as given by several Wranglers and Senior Optimes, in the Examination of Mathematical Tripos for Honours, 1868, January 13, 14, 15, 16, 17.

Number of Questions and Riders in the Printed Papers.

Questions. Riders. Aggregate.

In the 10 Papers of the 5 days 123 101 224

NUMBER OF QUESTIONS AND RIDERS ANSWERED.

Questions. Riders. Aggregate.

By a Wrangler, between the 1st and 7th 69-1/2 25-1/2 95 1 in 2.36 By a Wrangler, between the 12th and 22nd 48-1/2 12-1/2 61 1 in 3.68 By a Wrangler, between the 22nd and 32nd 36 12-1/2 48-1/2 1 in 4.62 By a Sen. Opt. between the 1st and 10th 17-1/2 5 22-1/2 1 in 9.95 By a Sen. Opt. between the 10th and 20th 14-1/2 2 16-1/2 1 in 3.60

G.B. AIRY.

_1868, March 12_.

ST PETER'S COLLEGE LODGE, CAMBRIDGE, _March 13th, 1868_.

MY DEAR SIR,

I am much obliged by your letter and enclosed paper.

Anything done in the last five days by a Junior Optime only shews (generally) that he has been employing some of his time _mischievously_, for he must have been working at subjects which he is quite unable to master or cramming them by heart on the chance of meeting with a stray question which he may answer.

The chief part of the Senior Optimes are in something of the same situation.

I think that the proposed addition of a day to the first part of the Examination, in which "easy questions in physical subjects" may be set, is, on this account, a great improvement.

Our new Scheme comes on for discussion on Friday next, March 20, at 2 p.m. in the Arts School. It is much opposed by private tutors, examiners and others, and may possibly be thrown out in the Senate this year, though I hope that with a little patience it may be carried, in an unmutilated form, eventually.

The enclosed Report on the Smith's Prize Examination will be discussed at the same time.

I will consider what is best to be done on the subject to which your note refers, without delay. With many thanks,

I am, Very faithfully yours, H.W. COOKSON,

_The Astronomer Royal._

In this year certain Members of the Senate of the University of Cambridge pet.i.tioned Parliament against the abolition of religious declarations required of persons admitted to Fellowships or proceeding to the degree of M.A. The doc.u.ment was sent to Airy for his signature, and his reply was as follows:

ROYAL OBSERVATORY, GREENWICH, LONDON, S.E.

_1868, March 18_.

MY DEAR SIR,

Though I sympathize to a great extent with the prayer of the pet.i.tion to Parliament which you sent to me yesterday, and a.s.sent to most of the reasons, I do not attach my signature to it, for the following considerations:

1. I understand, from the introductory clause, and from the unqualified character of the phrase "any such measures" in the second clause, that the pet.i.tion objects to granting the M.A. degree without religious declaration. I do not see any adequate necessity for this objection, and I cannot join in it.

2. It appears to me that the Colleges were intended for two collateral objects:--instruction by part of the Fellows, on a religious basis; and support of certain Fellows for scientific purposes, without the same ostentatious connection with religion. I like this spirit well, and should be glad to maintain it.

3. I therefore think (as I have publicly stated before) that the Master of the College ought to be in holy orders; and so ought those of the Fellows who may be expected to be usually resident and to take continuous part in the instruction. But there are many who, upon taking a fellowship, at once lay aside all thoughts of this: and I think that such persons ought not to be trammelled with declarations.

4. My modification of existing regulations, if it once got into shape, would I dare say be but a small fraction of that proposed by the "measures in contemplation." Still I do not like to join in unqualified resistance to interference in the affairs of the Established Colleges, with that generality of opposition to interference which the pet.i.tion seems to intimate.

I agree with articles 3, 4, and 5; and I am pleased with the graceful allusion in article 4 to the a.s.sistance which has been rendered by the Colleges, and by none perhaps so honourably as Trinity, to the parishes connected with it. And I could much wish that the spirit of 3 and 5 could be carried out, with some concession to my ideas in _my_ paragraph 3, above.

I am, my dear Sir, Yours very truly, G.B. AIRY.

_Rev. Dr Lightfoot._

1869

From the Report to the Board of Visitors it appears that application had been made for an extension of the grounds of the Observatory to a distance of 100 feet south of the Magnetic Ground, and that a Warrant for the annexation of this s.p.a.ce was signed on 1868, Dec. 8. The new Depot for the Printed Productions of the Observatory had been transferred to its position in the new ground, and the foundations for the Great Shed were completed.--"The courses of our wires for the registration of spontaneous terrestrial galvanic currents have been entirely changed. The lines to Croydon and Deptford are abandoned; and for these are subst.i.tuted, a line from Angerstein Wharf to Lady Well Station, and a line from North Kent Junction to Morden College Tunnel. At each of these points the communication with Earth is made by a copper plate 2 feet square. The straight line connecting the extreme points of the first station intersects that connecting the two points of the second station, nearly at right angles, and at little distance from the Observatory.--The question of dependence of the measurable amount of sidereal aberration upon the thickness of gla.s.s or other transparent material in the telescope (a question which involves, theoretically, one of the most delicate points in the Undulatory Theory of Light) has lately been agitated on the Continent with much earnestness. I have calculated the curvatures of the lenses of crown and flint gla.s.s (the flint being exterior) for correcting spherical and chromatic aberration in a telescope whose tube is filled with water, and have instructed Mr Simms to proceed with the preparation of an instrument carrying such a telescope. I have not finally decided whether to rely on Zenith-distances of gamma Draconis or on right-ascensions of Polaris. In any form the experiment will probably be troublesome.--The transit of Mercury on 1868, Nov. 4th, was observed by six observers. The atmospheric conditions were favourable; and the singular appearances usually presented in a planetary transit were well seen.--Mr Stone has attached to the South-East Equatoreal a thermo-multiplier, with the view of examining whether heat radiating from the princ.i.p.al stars can be made sensible in our instruments. The results. .h.i.therto obtained are encouraging, but they shew clearly that it is vain to attempt this enquiry except in the most superb weather; and there has not been a night deserving that epithet for some months past.--The preparations for observing the Transits of Venus were now begun in earnest. I had come to the conclusion, that after every reliance was placed on foreign and colonial observatories, it would be necessary for the British Government to undertake the equipment of five or six temporary stations. On Feb. 15th I sent a pamphlet on the subject to Mr Childers (First Lord of Admiralty), and in April I wrote to the Secretary, asking authority for the purchase of instruments. On June 22nd authority is given to me for the instruments: the Treasury a.s.sent to _10,500_. On August 9th I had purchased 3 equatoreals.--I have given a short course of Lectures in the University of Cambridge on the subject of Magnetism, with the view of introducing that important physical science into the studies of the University. The want of books available to Students, and the novelty of the subject, made the preparation more laborious than the duration of the lectures would seem to imply."--In this year there was much work on the Standards Commission, chiefly regarding the suggested abolition of Troy Weight, and several Papers on the subject were prepared by Airy.--He also wrote a long and careful description of the Great Equatoreal at Greenwich.

Of private history: There was the usual visit to Playford in the winter. Mrs Airy was now becoming feebler, and did not now leave Greenwich: since April of this year her letters were written in pencil, and with difficulty, but she still made great efforts to keep up the accustomed correspondence.--In April Airy went to Cambridge to deliver his lectures on magnetism to the undergraduates: the following pa.s.sage occurs in one of his letters at this time: "I have a mighty attendance (there were 147 names on my board yesterday), and, though the room is large with plenty of benches, I have been obliged to bring in some chairs. The men are exceedingly attentive, and when I look up I am quite struck to see the number of faces staring into mine. I go at 12, and find men at the room copying from my big papers: I lecture from 1 to 2, and stop till after 3, and through the last hour some men are talking to me and others are copying from the papers; and I usually leave some men still at work. The men applaud and shew their respect very gracefully. There are present some two or three persons who attended my former lectures, and they say that I lecture exactly as I did formerly. One of my attendants is a man that they say cannot, from years and infirmity and habit, be induced to go anywhere else: Dr Archdall, the Master of Emmanuel. I find that some of my old lecturing habits come again on me. I drink a great deal of cold water, and am very glad to go to bed early."--From June 10th-30th he was travelling in Scotland, and staying at Barrow House near Keswick (the residence of Mr Langton), with his son Hubert.--Subsequently, from Aug. 17th to 31st, he was again in the Lake District, with his daughter Christabel, and was joined there by his son Hubert on the 24th. The first part of the time was spent at Tarn Bank, near Carlisle, the residence of Mr Isaac Fletcher, M.P. From thence he made several expeditions, especially to Barrow in Furness and Seascale, where he witnessed with great interest the Bessemer process of making steel. From Barrow House he made continual excursions among the c.u.mberland mountains, which he knew so well.

1870

"In this year Mr Stone, the First a.s.sistant, was appointed to the Cape of Good Hope Observatory, and resigned his post of First a.s.sistant. Mr Christie was appointed in his place.--From the Report to the Visitors it appears that 'A few months since we were annoyed by a failure in the illumination of the 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-gla.s.s of a Reversed Telescope in the interior of the Transit-axis, and through which all illuminating light must pa.s.s, 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 princ.i.p.al 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 circ.u.mstances, 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 a.s.sistants 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 a.s.sistants 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 _530_. 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 pa.s.sed between 20h and 17h, with some observations for adjustment at a still more advanced time. As the astronomical lat.i.tude of the place of observation is not known, the bearing of these observations on the question of aberration cannot be certainly p.r.o.nounced until the autumn observations shall have been made; but supposing the geodetic lat.i.tude to be accordant with the astronomical lat.i.tude, 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 gla.s.s 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 a.s.sistants 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 repet.i.tion 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 repet.i.tion 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."