CHAPTER III. THE TOTAL ECLIPSE OF THE SUN Observations by Airy.—By Hind.—By Lassell. NE of the most important total eclipses of the Sun that have ONE occurred within the last few years was that of July 28, 1851. Though not visible in England, it was seen to great advantage in Sweden, to which country astronomers flocked in great numbers. From the numerous observations that were made and subsequently published, I select some extracts which will doubtless interest the reader. The following remarks are from the pen of Mr. G. B. Airy, the Astronomer Royal, who observed the eclipse at Göttenberg : "The approach of the totality was accompanied with that indescribably mysterious and gloomy appearance of the whole surrounding prospect, which I have seen on a former occasion. A patch of clear blue sky in the zenith became purple-black while I was gazing on it. I took off the higher power with which I had scrutinized the Sun, and put on the lowest power (magnifying about 34 times). With this I saw the mountains on the Moon perfectly well. I watched carefully the approach of the Moon's limb to that of the Sun, which my graduated dark glass enabled me to see in great perfection: I saw both limbs perfectly well defined to the last, and saw the line becoming narrower, and the curves becoming sharper, without any distortion or prolongation of the limbs. I saw the Moon's serrated limb advance up to the Sun's, and the light of the Sun glimmering through the hollows between the mountain peaks, and saw these glimmering spots extinguished one after another in extremely rapid succession, but without any of the appearances which Mr. Baily has described. I have no means of ascertaining whether the darkness really was greater in the eclipse of 1842. I am inclined to think, that in the wonderful, and I may say appalling obscurity, I saw the grey granite hills, within sight of Hvaläs, more distinctly than the darker country surrounding the Superga. But whether, because in 1851 the sky was much less clouded than in 1842 (so that the transition was from a more luminous state of sky, to a darkness nearly equal in both cases), or from whatever cause, the suddenness of the darkness in 1851 appeared to be much more striking than in 1842. My friends, who were on the upper rock, to which the path was very good, had great difficulty in descending. A candle had been lighted in a lantern, about a quarter of an hour before the totality; Mr. Hasselgren was unable to read the minutes of the chronometer's face without having the lantern held close to the chronometer. "The corona was far broader than that which I saw in 1842; roughly speaking, its breadth was a little less than the Moon's diameter, but its outline was very irregular. I did not remark any beams projecting from it which deserved notice as much more conspicuous than the others; but the whole was beamy, radiated in structure, and terminated (though very indefinitely) in a way which reminded me of the ornament frequently placed round a mariner's compass. Its colour was white, and resembling that of Venus. I saw no flickering or unsteadiness of light. It was not separated from the Moon by any dark ring, nor had it any annular structure: it looked like a radiating luminous cloud behind the Moon. The form of the prominences was most remarkable. One reminded me of a boomerang. Its colour, for at least two-thirds of its width, from the convexity to the concavity, was full lake red; the remainder was nearly white. The most brilliant part of it was the swell farthest from the Moon's limb; this was distinctly seen by my friends and myself with the naked eye. I did not measure its height; but judging generally by its proportion to the Moon's diameter, it must have been 3'. This estimation, perhaps, belongs to a later period of the eclipse. . . . It was impossible to see the changes that took place in the prominences, without feeling the conviction that they belonged to the Sun, and not to the Moon. "I again looked round, when I saw a scene of unexpected beauty. The southern part of the sky, as I have said, was covered with uniform white cloud; but in the northern part were detached clouds, upon a ground of clear sky. This clear sky was now strongly illuminated to the height of 30° or 35°, and through almost 90° of azimuth, with rosy red light shining through the intervals between the clouds. I went to the telescope, with the hope that I might be able to make the polarization-observation (which, as my apparatus was ready to my grasp, might have been done in 3 or 4 seconds), when I saw the sierra, or rugged line of projections, had arisen. This sierra was more brilliant than the other prominences, and its colour was nearly scarlet. The other prominences had perhaps increased in height, but no additional new ones had arisen. The appearance of this sierra, nearly in the place where I expected the appearance of the Sun, warned me that I ought not now to attempt any other physical observation. In a short time the white Sun burst forth, and the corona, and every other prominence, vanished. "I withdrew from the telescope, and looked round. The country seemed, though rapidly, yet half unwillingly, to be recovering its usual cheerfulness. My eye, however, was caught by a duskiness in the south-east, and I immediately perceived that it was the eclipse-shadow in the air, travelling away in the direction of the shadow's path. For at least 6 seconds this shadow remained in sight, far more conspicuous to the eye than I had anticipated "." Mr. J. R. Hind watched the eclipse at Rævelsberg, near Engelholm. He says: "The moment the Sun went out the corona appeared; it was not very bright, but this might arise from the interference of an extremely light cloud of the cirrus class, a Mem. R.A.S., vol. xxi. p. 8. which overspread the Sun at the time. The corona was of the colour of tarnished silver, and its light seemed to fluctuate considerably, though without any appearance of revolving. Rays of light, the aigrettes, diverged from the Moon's limb in every direction, and appeared to be shining through the light of the corona. In the telescope many rose-coloured flames were noticed; one, far more remarkable than the rest, on the western limb, could be distinguished without any telescopic aid; it was curved near its extremity, and continued in view 4 seconds after the Sun had disappeared, i. e., after the extinction of Baily's beads,' which phenomena were very conspicuous in this eclipse, particularly before the commencement of the totality. In this case they were clearly to be attributed to the existence of many mountains and valleys along the Moon's edge, the Sun's light shining through the valleys and between the mountain ridges, so as to produce the appearance of luminous drops or beads, which continued visible some seconds. The colour of the flames' was a full rose red at the borders, gradually fading off, towards the centres, to a very pale pink. Along the southern limb of the Moon, for 40° or upwards, there was a constant succession of very minute rose-coloured prominences, which appeared to be in a state of undulation, though without undergoing any material change of form. An extremely fine line, of a violet colour, separated these prominences from the dark limb of the Moon. The surface of our satellite, during the total eclipse, was purplish in the telescope; to the naked eye it was by no means very dark, but seemed to be faintly illuminated by a purplish grey light of uniform intensity, on every part of the surface. "The aspect of nature during the total eclipse was grand beyond description. A diminution of light over the Earth was perceptible a quarter of an hour after the beginning of the eclipse; and about ten minutes before the extinction of the Sun, the gloom increased very perceptibly. The distant hills looked dull and misty, and the sea assumed a dusky appearance, like that it presents during rain; the daylight that remained had a yellowish tinge, and the azure blue of the sky deepened to a purplish violet hue, particularly towards the north. But notwithstanding these gradual changes, the observer could hardly be prepared for the wonderful spectacle that presented itself, when he withdrew his eye from the telescope, after the totality had come on, to gaze around him for a few seconds. The southern heavens were then of a uniform purple-grey colour, the only indications of the Sun's position being the luminous corona, the light of which contrasted strikingly with that of the surrounding sky. In the zenith and north of it, the heavens were of a purplish-violet, and appeared very near; while in the north-west and north-east, broad bands of yellowish crimson light, intensely bright, produced an effect which no person who witnessed it can ever forget. The crimson appeared to run over large portions of the sky in these directions, irrespective of the clouds. At higher altitudes the predominant colour was purple. All nature seemed to be overshadowed by an unnatural gloom. The distant hills were hardly visible, the sea turned lurid red, and persons standing near the observer had a pale livid look, calculated to produce the most painful sensations. The darkness, if it can be so termed, had no resemblance to that of night. At various places within the shadow, the planets Venus, Mercury, and Mars, and the brighter stars of the first magnitude, were plainly seen during the total eclipse. Venus was distinctly seen at Copenhagen, though the eclipse was only partial in that city; and at Dantzic she continued in view 10 minutes after the Sun had reappeared. Animals were frequently much affected. At Engelholm, a calf which commenced lowing violently as the gloom deepened, and lay down before the totality had commenced, went on feeding quietly enough very soon after the return of daylight. Cocks crowed at Elsinborg, though the Sun was only hidden there 30 seconds, and the birds sought their resting-places, as if night had come on "." Mr. W. Lassell, who was stationed near the Trollhätten Falls, thus describes the total obscuration :— "I may attempt, but I cannot accomplish, an adequate description of the marvellous appearances, and their effect upon the mind, which were crowded into this small space of 3 minutes, an interval which seemed to fly as if it were composed of seconds and not of minutes! Perhaps a naked-eye observer would more fully grasp the awful effect of the sudden extinguishment of light,-the most overpowering of these appearances,-for, my eye being directed through the telescope, I must have been less, though sufficiently, struck with the unprecedented sensation of such instantaneous gloom. The amount of darkness may be appreciated from the fact that, on withdrawing my eye from the telescope, I could neither see the second hands of my watch, nor the paper sufficiently to write the time down; and was only able to do so by going to the candle, which I had by me burning on the table. Probably the suddenness of the gloom, not giving time for the expansion of the pupil of the eye, increased the sensation of apparent darkness; as I was obliged to repair close to the candle for the requisite light. After registering the time, I looked out for a few minutes with the naked eye over the landscape, north and south. The north was clear, and the line of horizon could be distinctly seen. The Sun, covered by the Moon, looking like a blue patch in the sky, had now the corona very symmetrically formed around it; but the Moon appeared to my unassisted eye to be not very round or smooth at its edge, -more as if one had rudely cut out with a knife on a board a circular disc of card,—the edges somewhat jagged and irregular in outline. "The corona itself was perfectly concentric and radiating, some of the rays appearing in some parts of the circumference a little longer than in others; but the inequality was not great. I am unable to say whether the corona when first found was at all eccentric, for, as it is evident that any one observing with a telescope up to the moment of obscuration must have time to take off the dark glass before the corona can be seen, and as I had also to note the time, the centres of the Sun and Moon must have been pretty closely approximating before I again applied the eye to the telescope. It was indeed a great exercise of self-denial to spare the time from the exciting phenomena, which was necessary for accurately recording the duration of total darkness; but being inclined to think such record would be disregarded by many observers, I took my resolution to secure it." The writer then proceeds to say that Venus was the only object visible to the naked eye. The corona he describes as brilliant," and he considers that it afforded, speaking roughly, as much light as the Moon usually does when at its full. "I had intended to direct my attention pointedly to the detection of the 'Red Flames,' which I had heard described as but faint phenomena. My surprise and astonishment may therefore be well imagined when the view presented itself instantly to my eye as I am about to describe, or rather to attempt to give a notion of. b Sol. Syst., p. 71. |