William Herschel and his work/Chapter 4

by James Sime

CHAPTER IV

THE DISCOVERY OF HERSCHEL

Herschel had been studying the stars with improved telescopes for upwards of four years before any of the literary and high-placed people, who flocked every winter to Bath, knew that a man of genius lived among them and was a servant to their gaiety or devotion. Beau Nash had been a better known figure in their streets, a more respected man among a community of fops, idlers, and intriguers, and was deemed more worthy of a statue in their pump-room or their public park.^[1] The man among them, who was destined to write his name on the heavens and to live when triflers and fops were all forgotten, attended their church meetings as an organist, their concerts as a conductor, and their drawing-rooms as a teacher of music to them or their children. They had not discovered that, by the irony of fate, a genius, head and shoulders above them all, was toiling for bread one half of the year, and slaving for fame or the welfare of mankind for the other half. He was really running two races before their eyes at the same time, the indispensable race for bread along one course, which they all saw and had little or no sympathy with, and the unquenchable race for fame along another totally unlike, to which they were altogether indifferent. To run both races at the same time required a spirit of indomitable energy and perseverance.

In the world of literature and science it is not unfrequently the hard fate of genius to be passed by in the crowd, till some onlooker discovers it, as a diamond may be discovered among a heap of common stones on the roadside. The fire of genuine inspiration may have warmed the heart or lighted up the eye; but, until the onlooker, long waited for, it may be, goes past, no difference will be seen between a genius and other men by the ordinary crowd of humanity.

Ministers of state, heads of political parties, busy-bodies filled with national affairs were seen, recognised, or pointed out in carriages or places of public resort by those who enjoyed or were compelled by doctors' orders to endure the weariness of the place.^[2] But "there are forty thousand others that I neither know nor intend to know," Walpole wrote: "in short, it is living in a fair, and I am heartily sick of it already." In the very year in which these words were written, Herschel was settled at Bath. He was one of the forty thousand nobodies, but Walpole was compelled in good time to reckon him a power in the world; he was only a poor player in the world's fair at Bath.

Court ladies and people of distinction knew William Herschel at Bath. They patronised him and his sister, got him pupils, and did what they could for him in the race for bread. But they had no idea that he was at the same time running a race for fame, or, to speak more correctly, was preparing to step into that arena. They would have smiled an incredulous smile had anyone said so to them. A music master and a director of concerts they could understand and appreciate as an inferior creature; but a man who pottered about reflectors and refractors, and looked at the moon from a back garden or a street, when the rest of the world had gone to bed, was beyond their comprehension, or probably came in for their pity. And yet it was on a street, and late at night, that the genius of Herschel was discovered by an inhabitant of Bath, a perfect stranger to him and his scientific pursuits. So curious is the romance of the discovery that it is best told in Herschel's own words.

"About the latter end of this month [December 1779] I happened to be engaged in a series of observations on the lunar mountains, and the moon being in front of my house, late in the evening I brought my seven-feet reflector into the street, and directed it to the object of my observations. Whilst I was looking into the telescope, a gentleman coming by the place where I was stationed, stopped to look at the instrument. When I took my eye off the telescope, he very politely asked if he might be permitted to look in, and this being immediately conceded, he expressed great satisfaction at the view. Next morning the gentleman, who proved to be Dr. Watson, jun. (now Sir William), called at my house to thank me for my civility in showing him the moon, and told me that there was a Literary Society then forming at Bath, and invited me to become a member of it, to which I readily consented." The house in front of which this discovery of an astronomer was made, was in River Street,^[3] and the discoverer of Herschel was Dr. Watson, a distinguished Fellow of the Royal Society of London,^[4] and a man of whom Herschel afterwards spoke in his printed papers with the highest respect and gratitude.

A look through a telescope in a street-observatory was not uncommon then even for a rising philosopher. As Humphry Davy "was passing through the streets one fine night, he observed a man showing the moon through a telescope. He stopped to look at the earth's satellite, and tendered a penny to the exhibitor. But the latter, on learning that his customer was no less a person than the great Davy, exclaimed with an important air, that 'he could not think of taking money from a brother-philosopher.'"

Dr. Watson and his father, Sir William Watson, were well-known members of the Royal Society. To the father in 1745 was awarded the Copley Medal for "surprising discoveries in electricity, exhibited in his late experiments." His portrait also is one of those in the Royal Society's keeping. The son became a Fellow in 1770. Like his father, he had a leaning towards the study of electricity. In 1756, when the Society honoured itself by electing Benjamin Franklin, "although not an inhabitant of this island," a Fellow, the certificate recommending that this be done was signed by the President and seven others, of whom W. Watson, the father, was one. In 1762, Dr. Watson in a letter to the First Lord of the Admiralty^[5] recommended that the navy should be supplied with lightning-conductors of a pattern he devised. The ships were furnished with them, but they were not a success, and sixty years elapsed before conductors of a suitable construction were fastened to the masts. Long before then the danger of powder magazines on land from lightning had been recognised and provided for, but not without something like civil war among the Fellows of the Royal Society. A committee, of which Franklin and Dr. Watson were members, reported strongly in favour of pointed conductors for the powder magazines at Purfleet. One member not only dissented, but formed a party, who wrote and acted in favour of blunt and against pointed conductors. Again a committee was appointed, of which Dr. Watson was a member, to put the matter to the test of experiment. Their conclusion was the same as before. Unfortunately, this was in 1777, at the height of the war with the American colonies. Party politics were at once dragged in to decide a purely scientific question. Franklin was in favour of the lightning-rods ending in points. Philadelphia also had been provided with them, and "not a single instance" of mischief from the severe thunderstorms experienced in that city had happened. That was enough with foolish people to condemn points and favour blunts. The Royal Society decided for points; all who voted on that side were counted friends of the American rebels, as the phrase then went. King George III. took the side of the blunts. When Franklin was informed of the King's action, he wrote from France: "The King's changing his pointed conductors for blunt ones is a matter of small importance to me. . . . For it is only since he thought himself and family safe from the thunder of Heaven that he dared to use his own thunder in destroying his own subjects." But George III. went further. He even endeavoured to make the Royal Society rescind their decision in favour of points. Sir John Pringle, the President,—a man who had been Professor of Moral Philosophy in Edinburgh, who was physician-extraordinary to the King and Queen, vir illustris de omnibus bonis artibus bene meritus,—when urged to use his influence against points and for blunts, manfully replied, "Sire, I cannot reverse the laws and operations of nature." A late^[6] addition to the story is that the King replied, "Perhaps, Sir John, you had better resign." That he did resign and withdraw to Edinburgh a year afterward, is certain: whether points and blunts had any influence in causing him to take that step is uncertain, but it can scarcely be doubted that the King's interference in a scientific quarrel had something to do with the censure passed on his generosity by Dr. Watson, the son, four years afterwards.^[7] Possibly, Dr. Watson shared the opinion of Franklin's friend, who wrote the epigram—

"While you, great George, for knowledge hunt,
And sharp conductors change for blunt,
         The nation's out of joint :
Franklin a wiser course pursues,
And all your thunder useless views
         By keeping to the point."^[8]

Dr. Watson's discovery soon bore fruit. Herschel had been carefully studying the planet Saturn since the spring of 1774. He had also been observing the mountains on the moon's face and making calculations of their height. Besides, he had been watching a variable star in the neck of the constellation called The Whale. Four months after his introduction to Dr. Watson, he communicated to the Royal Society through him two papers, which were read on May 11, 1780, and modestly described as by Mr. William Herschel of Bath. The first of the two was "On the Periodical Star in Collo Ceti." The paper in itself was not of much consequence, and it was on an old and well-worn subject;^[9] but it showed the books which had influenced him in his astronomical studies, as his sister had found by experience, and the carefulness with which he had for years been making observations on the stars. He had no desire to be considered an amateur. He was in thorough earnest, keeping a journal of what he saw in the skies, and carefully noting every change for future reference. On this Stella Mira, or Wonderful Star, as it was called from the "surprising appearances" it was known to present, and the changes it was found to undergo in 333 or 334 days, he made at least fourteen separate observations and measurements between October 20, 1777, and February 7, 1780. He was only feeling his way as a recorder of what he saw in the heavens. It was but a beginning, and he was forty-two years of age.

To do justice to this eager lover of nature, the object which he had in view when he began to make telescopes for himself, should not be forgotten. He wanted to see with his own eyes what others had seen in the heavens, he hoped to see more than they had seen, and at last he determined to build an instrument of such power as should penetrate the depths of space far beyond the boundaries man had at that time attained. His purpose was to see the heavens as the telescope had revealed them to the eyes of others; it was not to be an assistant in an observatory such as Greenwich, content to discharge the routine work of each day, or perhaps of each night. A telescope, a most powerful telescope, was the purpose deeply rooted in his mind; it was not to improve the instruments then in use, nor to systematise the work done in observatories. Perhaps he had a large share in doing both. He read the scientific world a lesson on the necessity of all-night as well as all-day work, which they stood much in need of learning. Great and valuable as was the work done at Greenwich then and previously, it was done at small expense to the nation. An astronomer-royal at £300 a year, an assistant at £70, and a kitchen-garden was the kailyard policy pursued by our country up to 1811. Remonstrances were presented to the Government of the day. The salary was then doubled, "thirty chaldrons of coals and one hundred pounds of wax candles" were asked for, and the enclosing of the kitchen-garden! Evidently the official mind had not grasped the idea that the astronomer-royal was no longer a fortune-telling interpreter of the heavens, as Kepler had been forced to become for bread! With one assistant all-night work was barely possible!^[10] The instruments in use may be judged of from "An Account of the Equatorial Instrument," or "mural quadrant," given to the Royal Society in 1793, twenty years after Herschel began his labours. The precision of observation among the ancients could not be trusted to within from five to ten minutes. Tycho Brahe reduced the probable limit of error to within one minute. Hevelius in the following century brought it down to fiften or twenty seconds, and in the century after it was reduced to seven or eight seconds.^[11] To entitle observations to any credit it was then felt that a probable error of more than a few seconds could not be admitted—or perhaps only a hundredth part of the errors unavoidable in the days of Hipparchus. In 1827, Sir John Herschel was able to say that he had "secured such a degree of precision that the stars cross the wire often on the very beat of the chronometer when they are expected." Clocks, transit-instruments, mural-circles may be said to have been in their infancy when Herschel began his work. He did not propose to work or measure with these as men do in an observatory. He was eager to see with a telescope; but he soon found that, if he was to do any good, he would require to observe and measure as well. He was one of a race of working astronomers of whom England had cause to be proud. They might be called, but they were not amateurs.

The second paper, read the same day, and headed "Astronomical Observations relating to the Mountains of the Moon," was more ambitious, and formed a better prelude to the path of discovery, on which Herschel would soon enter. He begins with an apology for attempting to ascertain the height of the lunar mountains, but a "knowledge of the construction of the moon leads us insensibly to several consequences, which might not appear at first; such as the great probability, not to say almost absolute certainty, of her being inhabited." He is equally certain that the moon rejoices in an atmosphere like the earth's.^[12] Passing over this scientific faith, in the meantime, as a heritage he received from the past but had not examined, we find him boldly venturing to dispute the conclusions arrived at by Galileo, Hevelius, and others of great name. Galileo had made the lunar mountains higher than any then known on the earth, five and a half miles; but Hevelius reduced this estimate to about three miles and a quarter. Herschel attacked the problem, armed with a telescope of six feet eight inches focal length, which he speaks of as "a very excellent instrument, equal to any that was ever made." He brought to it also the same "uncommon diligence and attention," which made up in some measure for the imperfect instruments of previous astronomers; and he had confidence in himself, in his eyesight, and in the goodness of the work he had done.

He was struck by the "deep shadows" cast by mountains on the moon's surface. Probably these shadows were then a puzzle to him. But he made one sagacious observation, which subsequent observers have developed into a view of the moon's face altogether different from what he started with. On Mona Lacer he writes: "I am almost certain there are two very considerable cavities or places where the ground descends below the level of the convexity, just before these mountains." The moon's face is now known to be pitted with hollows of great extent and depth. Herschel's predecessors called them seas and oceans, of which there are none on the moon. The hills and mountains that rise from these vast cavities do not at the utmost greatly exceed the estimate come to by Herschel, a mile and a half, or a mile and three-quarters in height. But if the height be reckoned above the hollow from which they rise, it may be nearer three times as much. We count the heights of mountains on the earth from the level of the sea. If we reckoned from the bottom of the ocean, our mountains will be found considerably to exceed in height those of the moon. It is now known that these cavities in the moon are from ten to seventeen thousand feet in depth, that they are surrounded by a great rampart or wall, a hundred, two hundred, or two hundred and fifty miles round, and that the mountains which rise from the floor of the cavity may be about a mile or a mile and a half high.^[13]

His study of the moon's face led him, two years after, to believe that, from his far-off station near Windsor, to which he had then removed from Bath, he was looking down one night into the depths of the boiling crater of a volcano in the moon. A discovery so singular was not a thing to publish till he had full assurance of its accuracy. Four years after, he believed he had obtained evidence sufficient to warrant publication. Others, well qualified to judge, were of the same opinion. Among them was a gentleman from the Göttingen Society, to which Herschel the year before had taken the King's present of a 10-feet reflector. Writing to a friend in Paris, that gentleman says:—

"May 30.

"Sir,—Mr. Herschel has lately made a discovery of the greatest consequence, of which I have had the good fortune to be an eye-witness. He had observed last month, one or two days after the new moon, in the dark part of it, three luminous points. Two of these points were near each other, and their light was pale and weak. The third, which he judged to be about three English miles in diameter, exhibited a much stronger and a redder light. This he compared to a burning coal covered with ashes. These points he immediately conceived to be burning mountains, the two first being either nearly extinguished or beginning to burn, and the other in a state of actual eruption. Mr. Herschel did not fail to communicate his observation to the Royal Society; and the philosophers in this metropolis waited impatiently for the next new moon, which would necessarily confirm the observation, because the eruption would probably not continue above a month, and consequently the phenomena would be then very different, if Mr. Herschel's conjecture was well founded. Friday last, the 18th, the first day of the new moon, several philosophical gentlemen attended Mr. Herschel at his house in the country; but the weather was too cloudy to permit any observation. The next day I did myself the honour to visit him, with two of my friends. Fortunately, the sky was perfectly clear. After having examined, during two hours, the enlightened part of the moon, by means of Mr. Herschel's astonishing instruments, of which it is impossible to form an adequate idea without having seen them, we directed the telescope to the dark part of this satellite, and the conjecture of this great astronomer was instantly confirmed. The two first-mentioned luminous points had totally disappeared, and the fire of the other was become pale and weak. The diameter of its crater was increased to about six miles. Next month it will probably be entirely invisible. This discovery of volcanoes in the moon is a proof that the matter of which it is composed is similar to that of our earth, and also proves the existence of a lunar atmosphere, which some philosophers have doubted. The science of astronomy is therefore infinitely indebted to the zeal of Mr. Herschel.

"This phenomenon was also seen by Count Bruhl, Mr. Cavendish, Mr. Aubert, etc.—Yours, etc., Z. Z."^[14]

Lalande, of the Royal College of France, told a somewhat more wonderful story to the scientific world in a paper which he wrote for the Academy of Dijon. "Herschel," he says, "has seen in the moon two peaks or mountains formed almost before his eyes; there are in their neighbourhood certain currents resembling those torrents of lava that flow from a volcano at the time of its greatest eruption. This observation was confirmed by an actual eruption very visible in his telescope of 9 feet: it is a fire or light like that of a star of the fourth magnitude seen by the naked eye, and it appeared on the obscure part of the moon. This may help to explain the observation of Ulloa, who, in the total eclipse of 1783, saw in the middle of the moon a luminous point, which he conjectured to be a perforation." Alas for the astronomers who probably saw what they devoutly wished to see—a volcano in action on the moon! It was all moonshine, apparently a reflection of light from our earth, when sixteen times the amount of light showered on us at full moon is then thrown by us on her! But a hole through the middle of the moon, perhaps twenty miles round! There is no air that we know of on the half of the moon that we see, and there is no water. There are ample traces of volcanic fires that once lighted her surface, but they are all long gone out, and have left nothing behind for us but insoluble problems and mysterious wonders—a world of craters, lava, precipices, and cinders. That astronomers were mistaken was no discredit to them. They stumbled in the race for knowledge. That was all. If the reports of moving masses, still said to be seen in the moon, be confirmed, there may not have been much of a stumble after all.

While the observatories of Europe took a serious view of these volcanoes and lava rivers in the moon, the wits of London, and the King's equerries at Windsor, were making fun of the whole thing, and turning the batteries of ridicule on William Herschel. Tea in the room of the wardrobe ladies at Windsor Castle, especially with Mr. Bryant, the antiquary and author in the company, "was extremely pleasant." It was always antiquities or odd accidents with him: "This night, Dr. Herschel and his newly discovered volcanoes in the moon came in for their share." Next evening three equerry colonels were at table. The volcanoes again came into the eyes or lips of some of the party. "I don't give up to Dr. Herschel at all," cried Colonel Manners; "he is all system, and so they are all; and if they can but make out their systems they don't care a pin for anything else. As to Herschel, I liked him well enough till he came to his volcanoes in the moon, and then I gave him up: I saw he was just like the rest. How should he know anything of the matter? There's no such thing as pretending to measure at such a distance as that." The company sat silent while this outburst of lava, which was at once both right and absurdly wrong, was coursing along the table. The lava had cooled, its heat was forgotten, when Colonel Welbred quietly interjected, "Sir Isaac Newton had been as much scoffed and laughed at formerly as Herschel was now; but, in return, Herschel, hereafter, would be as highly reverenced as Sir Isaac was at present." To it they again set. Someone remarked that "upon the heat in the air being mentioned to Dr. Heberden, he had answered that he supposed it proceeded from the last eruption in the volcano in the moon." "Ay," cried Colonel Manners, "I suppose he knows as much of the matter as the rest of them; if you put a candle at the end of a telescope, and let him look at it, he'll say, What an eruption there is in the moon!"

"But Mr. Bryant himself has seen this volcano from the telescope."

"Why, I don't mind Mr. Bryant any more than Dr. Heberden; he's just as credulous as t'other."

And thus the equerries wrangled at Windsor, while the rest of the world wondered or laughed at these volcanoes in the moon.^[15]

Herschel's belief in an atmosphere of the moon was a heritage, a traditional heritage from the past. Had he fully examined the grounds on which the tradition was based, he would have opened a field of inquiry that remained closed for nearly a century and a half. In the total eclipse of the sun which happened in Switzerland on the 12th of May 1706, the red flames and the corona, features of an eclipse now known to everybody, were observed, apparently for the first time. Captain Stannyan, who was at Berne with the British Envoy, wrote that very day: "The sun was totally darkened for 41/2 minutes of time; a fixed star and a planet appeared very bright; and his getting out of the eclipse was preceded by a blood-red streak of light, from its left limb; which continued not longer than 6 or 7 seconds of time;^[16] then part of the sun's disk appeared, all of a sudden, bright as Venus was ever seen in the night; nay, brighter, and in that very instant gave a light and shadow to things, as strong as moonlight uses to do." Flamsteed adds his own comment on this strange story: "The Captain is set down as the first man ever heard of that took notice of a red streak of light preceding the emersion of the sun's body from a total eclipse. And I take notice of it to you, because it infers that the moon has an atmosphere; and its short continuance of only 6 or 7 seconds of time, tells us that its height is not more than the 5 or 6 hundredth part of her diameter," that is, about four miles.

At Geneva the same eclipse was viewed by a friend of Sir Isaac Newton, Facio Duillier, who, apparently, did not see the "blood-red streak," but gives a good description of the Crown, or as it is now called, the Corona. "The clouds," he says, "did change of a sudden their colour, and became red, and then of a pale violet. There was seen, during the whole time of the total immersion, a whiteness, which did seem to break out from behind the moon, and to encompass it on all sides equally. The same whiteness was but little determined, in its outward side, and was not broad the twelfth part of the diameter of the moon. This planet did appear very black, and her disk very well defined, within the whiteness, which encompassed it about, and whose colour was the same with that of a white crown or halo, of about four or five degrees in diameter, which accompanied it, and had the moon for its centre. ... A little time after the sun had began to appear again, the whiteness and the crown, which did encompass the moon, did entirely vanish."^[17] Duillier's comment on this description of the corona is: "The moon's atmosphere cannot well be supposed less than of 130 miles, in perpendicular height. . . . Though it was very plain that the atmosphere of the moon must needs show itself, in the time of a total eclipse of the sun; yet I do not know that anybody did think of this, till in the last month of May, many persons did actually see it."^[18]

At Zurich Dr. Scheuchzer, in four lines of Latin, describes how they had a solar eclipse, at once total and annular; total, because the sun was wholly covered by the moon; annular, not properly so called, but by refraction, since around the moon appeared a ruddy brightness (fulgor rutilans), caused by rays refracted through the moon's atmosphere.

The blood-red streak, the corona, the ruddy brightness observed during the total eclipse of 1706, the doubts about the moon's atmosphere, and the difficulties experienced in accounting for the crown, "or else concerning a meteor observed, not in our air, but in the vapours that encompass the sun," might have warned Dr. Halley and others to be especially watchful when a total eclipse was due in Britain on April 22, 1715. Halley admitted the points named to be "very singular, and deserving a great deal of attention." He believed that a total eclipse of the sun had not been seen in London since March 20, 1140 A.D. He passes a gentle censure on the French astronomers for their indifference to the total eclipse of 1706, but excuses them on the ground that it was the first which "had been observed with the attention the dignity of the phenomenon requires." Strange to say, he made no preparation to watch for "the blood-streak" and "the luminous ring" that crowned the black body of the moon, when the chance of seeing them again was presented in 1715. They were seen and described by him with a singular turning aside from facts to fables about the moon's atmosphere, and the vapours that were raised or the dews that fell on her surface. Here is the account Halley gives of the red clouds and the luminous ring in the eclipse of 1715:^[19]—

"A few seconds before the sun was all hid, there discovered itself round the moon a luminous ring, about a digit, or perhaps a tenth part of the moon's diameter in breadth. It was of a pale whiteness or rather pearl colour, seeming to me a little tinged with the colours of the Iris, and to be concentric with the moon, whence I concluded it the moon's atmosphere. But the great height thereof far exceeding that of our earth's atmosphere; and the observations of some, who found the breadth of the ring to increase on the west side of the moon as the emersion approached, together with the contrary sentiments of those whose judgment I shall always revere, makes me less confident, especially in a matter whereto I own I gave not all the attention requisite.

"Whatever it was, this ring appeared much brighter and whiter near the body of the moon than at a distance from it; and its outward circumference, which was ill defined, seemed terminated only by the extreme rarity of the matter it was composed of; and in all respects resembled the appearance of an enlightened atmosphere viewed from far; but whether it belonged to the sun or moon I shall not at present undertake to decide.

"During the whole time of the total eclipse I kept my telescope constantly fixed on the moon, in order to observe what might occur in this uncommon appearance: and I found that there were perpetual flashes or coruscations of light, which seemed for a moment to dart out from behind the moon, now here, now there, on all sides; but more especially on the western side before the emersion; and about two or three seconds before it, on the same western side where the sun was just coming out, a long and very narrow streak of a dusky but strong red light seemed to colour the dark edge of the moon; though nothing like it had been seen immediately after the immersion. But this instantly vanished upon the first appearance of the sun, as did also the aforesaid luminous ring."^[20]

Halley adds to this beautiful description that the darkness was "more perfect," and the stars seen were more numerous, in some places than in others; but "the light of the ring was to all alike." From the north of England, too, he heard "that the luminous ring round the moon was seen there, which was nowhere visible but while the eclipse was total"! Nine years before Halley conjectured that the cause of the corona or ring lay, "probably, in those very vapours, which produce that pointed light, that has been observed lying in a manner along the ecliptic, and that has the sun for centre," the zodiacal light.

Into this traditional heritage of a lunar atmosphere Herschel passed, till the blindness of unreasoning belief was dispelled by facts. His atmosphere of the moon, his three volcanoes on its surface, and its fitness as a home for life, similar to what exists on the earth, were long cherished beliefs, that had all to be un-learned. Had the knowledge acquired from the total eclipses of the sun in 1706 and 1715 not been laid on the shelf and forgotten, he would not have fallen into these mistakes. Unfortunately, though twenty-eight solar eclipses occur every eighteen years somewhere on earth, no total eclipse has been seen from our island since 1716. A few years passed away, and, in 1792, Herschel came to the conclusion that we "have great reason to surmise that the moon's atmosphere," as well as that of Saturn's fifth satellite, is "extremely rare."

1. "At the east end of the saloon, a posthumous marble statue of the great Nash, executed by Prince Hoare, at the expense of the corporation, is handsomely ensconced" (Granville (in 1889), Spas of England, ii. 394).
2. See Walpole's Letters from Bath, v. 160, Oct. 2, 1766.
3. He soon afterwards removed to 19 New King Street.
4. Dr. Watson seems to have done a similar kindness to others. See Annual Register for 1783 [58-60].
5. Lord Anson (Phil. Trans., Dec. 16, 1762).
6. In 1820.
7. Sir John, after his return from Edinburgh to London in 1781, had the pleasure of spending a couple of hours on week-nights at a society of which he had been for many years a member, and where he met "with such friends as Mr. Cavendish, Dr. Heberden, and Dr. Watson." It was at one of these meetings that Sir John, on the 14th of January 1782, was seized with a fit from which he never recovered. In August of that year, with his friend's death still fresh in his thoughts, Dr. Watson gave expression to his sentiments regarding the King's shabbiness (Annual Register, 1783 [45]).
8. Weld, Hist. of the Royal Society, ii. 7, 94-101, 392.
9. See Lalande, i. 314 (edition 1771).
10. Weld, ii. 250.
11. Phil. Trans. for 1798.
12. In 1762, Samuel Dunn, from "a nice examination of the two ends of Saturn's ring, at such time when the planet is on the dark edge of the moon," came to the conclusion "that this diversity of appearance must have arisen from the effects of an atmosphere of the moon." Previously, he states, the existence of an atmosphere was much debated, and is "still undecided" (Phil. Trans. for 1761-2, vol. lii. p. 580).
    In a paper read before the Royal Society on November 27, 1766, the Prince de Croy expresses doubts about the existence of a lunar atmosphere, but "I am inclined to believe," he says, "there is no water in the moon." He also states that the hollows between the mountains marked on his diagram are surprising on account of their depth.
13. Moretus is a circular depression 120 kilometres across (80 miles), with an isolated mountain in the centre of nearly 7000 feet in height, the most considerable of its kind on the moon (Atlas Photographique de la Lune, Paris 1898, c. 56). The depths of the cavities are frequently very great, Tycho, for example, 5500 metres, or nearly 18,000 feet (c. 30, c. 55). Some of the mountain masses or tablelands are 5000 metres, 6600, and 7100, judging from the shadows they cast, or 16,000, 21,000, or 28,000 feet (c. 55, 56).
14. Scots Magazine vol. xlix. 318, quoted from Gentleman's Magazine.
15. Miss Barney, Letters, iii, 375-380.
16. In the total eclipse of the present year there was seen "a brilliant display of carmine-coloured prominences extending over an arc of at least 60 deg." (Times, June 1, 1900, p. 10).
17. A letter from a friend at Marseilles informed Duillier that, during totality, "there did remain one bright digit, all about the globe of the moon" (Phil. Trans. (No. 306), p. 2237).
18. "The red prominences were first seen during the solar eclipse of 8th July 1842" (Proctor, Encyc. Brit., vol. ii. p. 788). Baily was not the first to see them. Captain Stannyan and Dr. Scheuchzer carried off the honour 136 years earlier. Facio Duillier has the credit of first describing the corona.
19. "Dews," Phil. Trans. xxix. p. 248.
20. On the eclipse of July 7 (8), 1842, Baily writes: "The breadth of the corona from the circumference of the moon was nearly equal to half of the moon's diameter. Its colour was quite white, not pearl colour, nor yellow, nor red, and the rays had a vivid and flickering appearance, somewhat like that which a gas-light illumination might be supposed to assume if formed into a similar shape" (Astron. Trans. xv. p. 5).
    Halley's account of what he saw in 1715 is as distinct and vivid as that of Baily in 1842. See also Lalande, ii. 443.