APPENDIX A.
ROYAL ASTRONOMICAL SOCIETY.
[For my Biography, written, chiefly from my dictation, in June, 1874.]
Although a member of the Astronomical Society for more than half a century, and, with the exception of two out of about 430, the oldest now living, I have never contributed to the Society’s transactions.
Yet from boyhood I have been very much attached to astronomical pursuits. My father was well informed on the subject, and eventually, though several years later than myself, became a member of the Society.[364] He had long possessed a reflecting telescope, capable of showing Jupiter’s Moons and Belts, and Saturn’s Rings, though not, according to my recollection, any of the moons, even the rings appearing not severally but as one. He had also a Hadley’s Quadrant, an artificial horizon, and a tolerably good clock, and he regularly took in the “Nautical Almanac.”
By means of this simple apparatus, he not only regulated the clock, but determined the latitude and even the longitude of our house, or rather of the playground, at Hill Top.
In these occupations I was invariably his assistant; and it was in this manner and with the aid of his lectures that I gradually acquired, even while a boy, a taste for Astronomy, and, for my age, no inconsiderable knowledge of the subject.
My father (like myself in youth and early manhood) was a great walker, and we frequently journeyed together. When I was only nine years of age, I walked with him, for the most part after dark, from Birmingham to Stourbridge, a distance of twelve miles, with occasional lifts—no doubt according to usage—on his back. I recollect that it was a brilliant starlight night, and the names of the constellations and of the brighter single stars, their apparent motions and the distinction between the so-called fixed stars and planets, formed then, as on many other similar occasions, never-failing subjects of interesting conversation, and to me of instruction. On the way we passed by the side of a small pool, and, the air being still, the surface of the water gave a perfect reflection of the stars. I have a vivid recollection, after an interval of nearly seventy years, of the fear with which I looked into what appeared to me a vast abyss, and of my clinging to my father to protect me from falling into it.
The remarkable comet of 1811—remarkable from the length of time it continued in sight—interested me greatly. I was then fifteen years of age. I examined it frequently with our telescope, got much information from my father and from such books as were accessible to me; and before the comet had disappeared was, I believe, tolerably familiar with what was then known of cometary astronomy.
As already stated in the “Prefatory Memoir,” the teaching of a subject was with me concurrent, or nearly so, with the learning. I soon began to lecture on Astronomy, first to the boys of our school, and afterwards to a literary and scientific association of which I was a member.
With a view to these lectures, availing myself of the “Transactions of the Royal Society” (taken in by one of the Birmingham libraries to which we subscribed), I read, I believe without exception, all the contributions of Sir William Herschel, then incomparably the first of living English astronomers. My reverence for the man led me to contrive, on the occasion of my second visit to London (1815), to go round by Slough, in order that I might obtain a glimpse—as the coach passed—of his great telescope, which I knew could be seen over the tops of the neighbouring buildings.
In the “Prefatory Memoir” I have already spoken of my teaching navigation, of the planispheres which I constructed for my father’s lectures upon electricity, of my trigonometrical survey, of my visit to Captain Kater and the Greenwich Observatory, and of my Vernier pendulums—all more or less intimately connected with my pursuit of Astronomy. Nor must I omit mention of a popular explanation of the transit of Mercury in May, 1832, which I wrote for the “Penny Magazine.” (See Vol. I., p. 82.)
I may also mention, as a fact worth recording, that in 1817 (I believe) the celebrated mathematician, M. Biot, passed through Birmingham on his return from the Shetland Isles, where he had been engaged in measuring an arc of the meridian.[365] My father was invited to dine with him, I think at the house of Mr. Tertius Galton; and afterwards both he and I, among others, were invited to meet him at the rooms of the Philosophical Institution. Very few obeyed this second summons, perhaps because the day fixed upon was Sunday. He showed us in action a small instrument for the polarization of light—a subject of which my father and I, and I think the others, were up to that time profoundly ignorant. The only individual with whom M. Biot appeared to be previously acquainted was an emigré, Dr. De Lys, a leading physician of Birmingham, whose father, the Marquis De Lys, had been guillotined during the Reign of Terror. In the evening we met again at a coach office in the Market Place, to bid farewell to M. Biot on his departure for London, when he caused some tittering, and put poor Dr. De Lys to the blush by publicly kissing him, in French fashion, on both cheeks.
To return to the Astronomical Society. My attendance at its meetings, so long as I continued to live near Birmingham, was necessarily rare. On my removal to the neighbourhood of London it became more frequent, but even then my time was so fully occupied with more pressing duties that my attendance remained very irregular, and it totally ceased several years ago. I have, however, invariably read the “Monthly Notices” of the Society’s proceedings, and have thus benefited more, perhaps, than by mere attendance.
Still, as already stated, I have never contributed to the Society’s transactions, the truth being that up to the time of my becoming disabled for steady application to any difficult subject, my mind was so entirely engrossed with my official duties, that the little leisure I could obtain was necessarily devoted to recruiting my health.
Nevertheless, as already shown,[366] I have attempted something to promote my favourite science. The following is an instance of the kind:—
VARIABLE STARS.
On the 16th January, 1865, I addressed the following letter to my late excellent friend, Admiral Smyth:—
“My dear Admiral,—I have just completed the perusal of your very interesting volume on ‘The Colours of Double Stars,’ kindly presented to me by Dr. Lee in your name and his; and I thank you for the gratification it has afforded me.
“What you say on the subject of variable stars has called to my recollection an idea which first occurred to me shortly after the discovery of the periodicity of the increase and decrease in the number and frequency of solar spots. I am aware that such increase and decrease is not continuous, and that the variation is not such as materially to affect the Sun’s brightness. Still, in point of fact, is not our own Sun a variable star—however slightly—with a period, tolerably well defined, of about eleven years? And may not the more marked character of other variable stars be owing to similar causes to those which produce the spots in our sun, acting with greater regularity and intensity?
“If you think it deserving attention, pray favour me with your opinion of my theory. Possibly it may have been suggested previously, but if so, I am not aware of the fact.
“I remain, my dear Admiral, yours faithfully,
“Rowland Hill.
“Admiral Smyth, F.R.S., &c., &c., &c.”
Shortly afterwards I received a very friendly letter from Mrs. Smyth, the tenor of which will be sufficiently understood from what follows:—
“Hampstead, 20th January, 1865.
“Dear Mrs. Smyth,—Many thanks for your letter. Pray don’t let the Admiral withdraw himself from his present work. My theory can wait, or I may find an opportunity of consulting some other authority.
“Our kindest regards.
“Very truly yours,
“Rowland Hill.”
I accordingly, on the 14th February following, addressed a letter—similar to the one to Admiral Smyth—to my friend, Mr. Warren De La Rue, then President—as Admiral Smyth had once been—of the Astronomical Society; but although Mr. De La Rue took much trouble to ascertain whether my theory had, as he thought, been suggested before, it was not till long afterwards that he was able to give any definite information on the subject.
In a letter of July 9th, 1866, Mr. De La Rue drew my attention to a paper by Mr. Balfour Stewart in the Transactions of the Royal Society of Edinburgh, which, in the opinion of Mr. De La Rue, “gives a very explicit enunciation” of the theory.
On referring to the paper in question (Vol. XXIII, part iii.), I found that it was read on the 18th April, 1864, and the following is an extract from a memorandum which I made on the subject:—“Indirectly, by showing a probable connexion between the maxima and minima of Sun-spots and the rotation of Jupiter about the Sun, and by suggesting that the periodic variations of the stars is caused by the rotation of large planets about them, Mr. Balfour Stewart has, I think, forestalled me.” Perhaps, however, I may be justified in doubting whether the enunciation here given is very explicit.
Before proceeding, it is necessary to digress for a moment. When a boy I was fond of reading books of elementary science. I occasionally met with statements which puzzled me—which appeared to me to be wrong—but assuming, as children do, the infallibility of the author—or perhaps I should say of a printed book—I naturally came to the conclusion that my own understanding was in fault, and became greatly disheartened. After awhile—I forget on what occasion—I applied for solution of the puzzle to my father, who, possessing a large amount of general information, was well qualified to advise. To my great delight, he assured me that I was right and the author wrong. My unqualified faith in printed statements was now, of course, at an end; and a habit was gradually formed of mentally criticising almost everything I read—a habit which, however useful in early life, is, as I have found in old age, a cause of much waste of thinking power when the amount is so reduced as to render economy of essential importance.
Still, through the greater part of my life this habit of reading critically, combined as it was with the power of rapid calculation, has been of great use to me, especially in my contests with the Post Office, and, after I had joined the Department, in the revision of the thousands of Reports, Returns, and Minutes prepared by other officers.
In general literature, if the author attempt to deal with science, the chance of a blunder appears to be great. Even Lord Macaulay could not always do so with safety, as appears from the following passage:—“In America the Spanish territories [in 1698] spread from the equator northward and southward through all the signs of the Zodiac far into the temperate zone.”[367] What can be the meaning of the words which I have marked for Italics?
Mrs. Oliphant, too, whose admirable stories I never miss reading, says, in one of her latest, “there was a new moon making her way upwards in the pale sky.”[368]
There is no writer to whom I feel more grateful than to Miss Edgeworth. When a boy I read her delightful stories with the greatest possible interest, and I feel sure that they had considerable influence in the formation of my character. Unfortunately, however, they are frequently disfigured by scientific errors. Thus, in her admirable story of “The Good Aunt,” the following passage occurs: “My dearest Aunt,” cried he [Charles], stopping her hand, as she was giving her diamond ear-rings to Mr. Carat—“stay, my dearest aunt, one instant, till I have seen whether this is a good day for selling diamonds.”
“O, my dear young gentleman, no day in the Jewish calendar more proper for de purchase,” said the Jew.
“For the purchase! yes,” said Charles, “but for the sale?”
“My love,” said his aunt, “surely you are not so foolish as to think there are lucky and unlucky days.”
“No, I don’t mean anything about lucky and unlucky days,” said Charles, running up to consult the barometer; “but what I mean is not foolish indeed; in some book I’ve read that the dealers in diamonds buy them when the air is light, and sell them when it is heavy, if they can, because their scales are so nice that they vary with the change in the atmosphere.”
Now, as the metallic weights are of greater specific gravity than the diamonds, the interests of the dealers—so far as they are affected by change of atmosphere—must be to buy when the air is heavy and sell when it is light. An increase of density in the air would, of course, reduce the gravity of both diamonds and weights, but not equally: the diamonds, being the more bulky, would lose gravity more than the weights, and consequently would weigh less. If it were possible that the air should increase in density till it became as heavy, bulk for bulk, as the diamonds, they would float therein, or, in other words, weigh nothing at all.
I well remember when, as a boy, I first read this admirable story, how much I was puzzled by the mistake in question.
An error, occasionally met with in novels, is as follows. A wonderful marksman has to exhibit his powers, which he does thus:—He throws into the air two birds—or perhaps inanimate objects—as two apples; then, waiting till both are in a line with himself, sends his arrow or bullet through both. A slight consideration will show that, in a vast majority of cases, no amount of waiting would suffice.
Another prevailing error is, that a person simply standing by the side of a pool can see his own reflection from the surface—Narcissus must have found some support which enabled him to lean over the fountain.
But it is in books especially intended to teach elementary science that such errors are most to be regretted.
A few years since I purchased for some of my grandchildren the eighth edition of “The Seasons,” by Mrs. Marcet. It is an admirable work, highly interesting and useful; but before placing it in the hands of my grandchildren, I thought it necessary to read it myself—a very pleasing task, by-the-by—and to correct any errors I might find. As examples, I may mention that in Volume I. snow is described as frozen rain; that in Volume IV. both stones in a flour-mill are said to revolve; and that the description in the same volume of a marine steam engine is very incorrect.
Again, few books are better calculated to interest boys than Dr. Parris’s “Philosophy in Sport,” but when, in the year 1829, I bought a copy for the School-Library at Bruce Castle, I found it necessary, before placing it there, to make numerous corrections to which I drew the attention of the author, who, in a letter dated March 18th, 1829, still in my possession, thanks me for my communication, and admits some of the errors, though not all.
As a specimen of the admitted errors, I give the following:—“Mr. Seymour now informed his young pupils that he had an experiment to exhibit, which would further illustrate, in a very pleasing manner, the truth of the doctrine of vis inertiæ. He accordingly inverted a wine-glass, and placed a shilling on its foot; and having pushed it suddenly along the table, the coin flew off towards the operator, or in a direction opposite to that in which the glass was moving.”[369]
My correction is as follows: “The coin would fall nearly in a perpendicular direction, but inclined a little towards the direction in which the glass was moving, owing to the friction between the glass and coin.”
As a specimen of the non-admitted errors, I give the following: “He had ignorantly fired a quantity of oxygen and hydrogen gases in a tin vessel; the consequence of the combustion was the immediate formation of a vacuum; and what happened? Why, the pressure of the external air, not being any longer balanced by elastic matter in the interior of the apparatus, crushed it with violence, as any other enormous weight might have done; and so ended the accident, which report magnified into a most awful catastrophe.”[370]
My correction is as follows: “The first effect of the combustion was to expand the air in the vessel, and this expansion it was that caused the accident.”
On which the author, after quoting my correction, replies, “Now you will allow me to say that here you have fallen into an error; I am perfectly correct in saying that the accident arose from the external pressure of the atmosphere; for remember that the vessel contained a mixture of oxygen and hydrogen gases, which, by combustion, immediately combined and formed water, leaving an almost perfect vacuum in the interior.”
If any one entertain a doubt as to which of us is correct, I would suggest his filling a small bladder with the proper mixture of oxygen and hydrogen, and exploding it by electrical means; as I did nearly sixty years ago. The bladder will be destroyed; but, according to Dr. Parris’s view, it should simply collapse.
But even men of unquestionable scientific knowledge are not always correct. The late Professor Phillips, in his able and interesting Address as President of the British Association in 1865, after noticing Foucault’s recent admeasurement of the velocity of light, proceeded as follows:—“By this experiment the velocity of light appears to be less, sensibly less, than was previously admitted; and this conclusion is of the highest interest. For, as by assuming too long a radius for the orbit of Jupiter, the calculated rate of light-movement was too great; so now, by employing the more exact rate and the same measures of time, we can correct the estimated distance of Jupiter and all the other planets from the Sun.”[371]
Professor Phillips’s great forte was geology, not astronomy. To any one familiar with the means by which Römer determined the velocity of light, it is unnecessary to point out that, although his observations were made on the satellites of Jupiter, the radius of Jupiter’s orbit has nothing to do with the problem. The only material facts are, first, the difference between the maximum and minimum distance of Jupiter from the earth,—that is to say (disregarding eccentricity) the diameter of the earth’s orbit; and, secondly, the effect which this varying distance has on the times at which the eclipses apparently take place. This effect Römer found to extend to about 16 minutes—and he thence concluded that light occupied 16 minutes in travelling across the earth’s orbit.
With the view of rendering the above intelligible to those not familiar with the subject, I offer the following illustration:—Suppose it to be known that about a certain hour a gun will be fired at a remote spot, the direction of which, but not the distance, is known, and that two persons (A. and B.) arrange to avail themselves of the opportunity for ascertaining, approximately, the velocity of sound; then, each being furnished with a good watch marking seconds, A. places himself at a certain spot, and B. at a known distance—say a mile—from A., and in a direction opposite to that of the gun, so that B.’s distance from the gun shall be a mile greater than A.’s—the actual distance in either case is unimportant.
Each now records the exact moment at which he hears the report; and if the gun be fired repeatedly, several such records are made, in order to give a more accurate result.
A. and B. then meet and compare notes. They, of course, find that A.’s time is in each instance earlier than B.’s. The average of the several differences would be about 4¾ seconds—showing that sound travels a mile in that time.[372]
The mode of procedure here described is, of course, not that actually adopted for determining the velocity of sound, but it is a practicable mode, and is selected because it is analogous to that adopted by Römer for determining the velocity of light.
A copy of Professor Phillips’s Address was sent to me immediately after its delivery, and, on my detecting the error, I endeavoured to induce a friend of his, deservedly eminent as a practical astronomer, to draw the Professor’s attention thereto, with a view to its correction before the publication of the permanent report of the Society’s proceedings; but, unfortunately, the attempt did not succeed.
In another similar case, however, as appears by the following correspondence between the Astronomer Royal and myself, I was more successful:—
“Hampstead, N.W.
“1868—June 17.[373]
“My dear Sir,—Pray accept my thanks for the copy of your Report. It came while I was at Brighton; but, since my return home, I have read it with great interest. I felt it a great privation not to be able to attend the Visitation.
“Will you allow me to request your attention to what appear to me to be serious errors in the recent annual Address of the President of the Astronomical Society? They will be found in the last paragraph of page 119 of the ‘Monthly Notices’ for February. To save you trouble, I have extracted the part in question, and have underlined the words which I think erroneous. ‘At the present time the Earth is about three millions of miles nearer to the Sun in our northerly winter than in our summer; our coldest month is about 60° Fh. colder than our hottest, and our winter lasts for about eight days longer than our summer. M. Leverrier has calculated that 200,000 years ago the Earth approached the Sun by upwards of ten millions of miles nearer in winter than in summer: the winters were then nearly a month longer than the summers, and in the latitude of London there was a difference of about 112° Fh. between the hottest and the coldest periods of the year.’
“If you find that I am right, perhaps you will have the kindness to draw Mr. Pritchard’s attention to the errors, with a view to their correction before the Address is printed in the ‘Transactions.’ I would write to Mr. Pritchard myself, but that, as I could not speak with authority, I might give offence.
“I have watched the subsequent monthly numbers in the expectation of finding a correction, but none has appeared.
“Faithfully yours,
“Rowland Hill.
“The Astronomer Royal, &c., &c., &c.”
The Astronomer Royal promptly replied as follows:—
“Royal Observatory, Greenwich, London, S.E.
“1868—June 18.
“My dear Sir,—I will duly bring before Mr. Pritchard the substance of your note of yesterday.
“The two clauses which you have cited are, on the face of them, erroneous; and in the first the fault clearly is in the word longer. In the second, the fault may be in the word nearer. For, during the period through which the great eccentricity prevails, the semi-revolution in the precession of the equinoxes may have reversed the seasons.
“It would seem that Mr. Pritchard has had in view the table in ‘Lyell’s Principles of Geology,’ Vol. I., p. 293. In the notes continued on p. 294, the references are to the case of winter in aphelion.
“The subject is a thorny one, but well worth your attention.
“I am, my dear Sir, yours very truly,
“G. B. Airy
“Sir Rowland Hill, K.C.B., &c., &c., &c.”
I am not aware how the passage in question stands in the Society’s Transactions.[374]
The following narrative seems to show that in a progressive science like Astronomy even the highest authority is not infallible.
Some sixty years ago, my attention having been accidentally drawn to a tide-mill for grinding corn, I began to consider what was the source of the power employed, and came to the conclusion that it was the momentum of the earth’s revolution on its axis. The next question I asked myself was—could such power be diverted, in however slight a degree, without drawing, as it were, on the stock? Further consideration showed me that the draught required for grinding the corn was trifling in comparison with that employed in grinding the pebbles on every seashore upon the earth’s surface; and, consequently, that the drain on the earth’s momentum might suffice in the course of ages to effect an appreciable retardation in the earth’s diurnal revolution.
I now, as usual in case of difficulty, applied to my father. He could detect no fault in my reasoning, but informed me that Laplace had demonstrated in his great work (“La Mécanique Céleste”) that the time occupied in the earth’s diurnal revolution is absolutely invariable. Of course both my father and I accepted the authority as unquestionable; but I never could fully satisfy my mind on the subject, and for the greater part of my life it was a standing puzzle.
It may be stated briefly that Laplace’s demonstration appears to have rested mainly on the fact that his Lunar Tables, if employed in calculating backwards certain eclipses of the Sun which happened about 2,000 years ago, give results agreeing so nearly with the ancient records as altogether to exclude the possibility of any appreciable increase in the length of the sidereal day during that long period.
But in the year 1866 Professor Adams (really the first discoverer of the planet Neptune) received the Gold Medal of the Astronomical Society for, among other recent claims, the discovery of an error in the data on which Laplace constructed his Lunar Tables which vitiates the above demonstration.
The details of this important discovery—and the co-operation therein of M. Delaunay—were fully and ably stated by Mr. Warren De La Rue, then President of the Society, on the presentation of the Medal.[375] And the position of the question two years later is concisely stated as follows by the Rev. Charles Pritchard, in an Addendum to his address as President in 1868:—“At present, then, the case stands thus,—the Lunar Tables, if calculated on the principles of gravitation alone, as expounded by Messrs. Adams and Delaunay, and as confirmed by other mathematicians, will not exactly represent the moon’s true place at intervals separated by 2,000 years, provided the length of the day is assumed to be uniform and unaltered during the whole of the intervening period. There are grounds, however, for at least suspecting that, owing to the effects of tidal action, the diurnal rotation is, and has been, in a state of extremely minute retardation; but the mathematical difficulties of the case, owing greatly to the interposition of terrestrial continents, are so great that no definite quantitative results have hitherto been attainable. The solution of the difficulty is one of those questions which are reserved for the Astronomy of the future.”[376]
I need not say that this confirmation of the truth of my early conjecture proved highly gratifying. I have only to add that the increase during the last 2,000 years in the length of the sidereal day is generally estimated at about the eightieth part of a second; but the estimate has, I apprehend, no better foundation than this—namely, that since the recent correction in the Lunar Tables an assumed increase to the extent in question has become necessary in order to make the backward calculation of the ancient eclipses agree with the records as to time.
I have found it very difficult at my age (little less than fourscore), and with my mental powers seriously impaired, to deal, however imperfectly, with a subject so abstruse as that now under consideration; and I think it by no means improbable that there may be some error in my statement of facts or in my argument thereon.
All that I can say is that I have done my best to render intelligible to ordinary readers an important advance in modern Astronomy—interesting in itself, irrespective of its remote and accidental connection with my own biography.
The following very gratifying letter from the Astronomer Royal may perhaps be appropriately given here. It is in reply to my congratulations when, in recognition of his great public services, he was made a K.C.B.:—
“Flamsteed House, Greenwich Park, London, S.E.
“1872—June 22.
“My dear Sir,—I could scarcely have had a more gratifying letter in reference to the public compliment just paid to me from any one than that from yourself. I can truly say that it has been my secret pride to do what can be done by a person in my position for public service; and whose recognition of this can be more grateful than that of one who—by efforts in a similar strain, but on an infinitely larger scale—has almost changed the face of the civilized world?
“My wife (I am hesitating between two titles, not knowing which is at the present moment correct, but being quite sure of that which I have written) begs me to convey to you her acknowledgment of your kind message.
“I am, my dear Sir, very truly yours,
“G. B. Airy.”