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that the motions of the spots do not correspond to this hypothesis, but point clearly to the conclusion that the Sun rotates on his axis in about a month, Scheiner re-examined his hypothesis, and presently admitted that Galileo was in the right. He then made a long and elaborate series of observations in order to deterDigression of Ayre. The following passage from this chapter is sufficiently apropos, and will, I doubt not, interest the curious reader :

In the meantime, the world is tossed in a blanket amongst them; they hoyse the earth up and down like a ball, make it stand and goe at their pleasures. One saith the sun stands; another, he moves; a third comes in, taking them all at rebound; and, lest there should any paradox be wanting, he findes certain spots and cloudes in the sun, by the help of glasses, which multiply (saith Keplerus) a thing seen a thousand times bigger in plano, and make it come 32 times neerer to the eye of the beholder: but see the demonstration of this glass in Tarde, by means of which, the sun must turn round upon his own center, or they about the sun. Fabritius puts onely three, and those in the sun Apelles, 15, and those without the sun, floating like the Cyanean isles in the Euxine sea. Tarde the Frenchman hath observed 33, and those neither spots nor clouds, as Galileus (Epist. ad Velserum) supposeth, but planets concentrick with the sun, and not far from him, with regular motions. Christopher Schemer [Scheiner] a German Suisser Jesuit, Ursica Rosa [Qy., in his Rosa Ursina], divides them in maculas et faculas, and will have them to be fixed in solis superficie, and to absolve their periodicall and regular motion in 27 or 28 dayes; holding withall the rotation of the sun upon his center; and are all so confident, that they have made skemes and tables of their motions. The Hollander, in his dissertatiuncula cum Apelle, censures all; and thus they disagree amongst themselves, old and new, irreconcileable in their opinions; thus Aristarchus, thus Hipparchus, thus Ptolomæus, thus Albateginus, thus Alfraganus, thus Tycho, thus Ramerus, thus Roslinus, thus Fracastorius, thus Copernicus and his adherents, thus Clavius and Maginus, &c., with their followers, vary and determine of these celestial orbs and bodies; and so, whilest these men contend about the sun and moon, like the philosophers in Lucian, it is to be feared the sun and moon will hide themselves, and be as much offended as shee was with those, and send another message to Jupiter, by some new fangled Icaromenippus, to make an end of all those curious controversies, and scatter them abroad.'

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mine the true period of rotation and the actual position of the solar axis of rotation. In his Rosa Ursina' (a most monstrous volume)* he published the results of his labours. He assigned to the Sun a rotation period of between twenty-six and twenty-seven days. He also stated that the plane of the Sun's equator is inclined between 6° and 8° to the plane of the ecliptic,— a very creditable result considering his means of observation, since the best modern measures assign 73° as the value of this angle.

Scheiner, Galileo, and Hevelius would seem to have independently recognised the fact that the solar spots are not of uniform brightness, but commonly surrounded by a fringe less dark than the central part. The last-named astronomer also recognised the existence of certain bright streaks in the neighbourhood of the spots. He called these the faculæ.

* Yet not meriting the disparaging comments of Delambre, who says, There are few books so diffuse and so void of facts. It contains 784 pages; there is not matter in it for fifty.' The prolixity, however, belongs to the age in which Scheiner lived, and is by no means peculiar to him. By a similar mode of judging, we should be entitled to hold in derision the works of Kepler. Lalande thus writes respecting Scheiner. Quoi qu'il en puisse être de celui à qui le hasard a fait voir les taches pour la première fois, il est sûr que personne ne les observa aussi bien et n'en donna la théorie d'une manière aussi complète que Scheiner. Son ouvrage a 774 pages sur cette matière, et cela suffit pour faire voir avec quelle assiduité il s'en occupa, et combien il donna d'étendue à ses recherches. Hévélius le cite avec le plus grand éloge: "Incomparabilis et omnigenæ eruditionis . . . . ut in hac materia omnibus palmam quasi præripuisse dici posset."' So much it has seemed fitting to say respecting a most laborious and ingenious investigator, whose valuable researches into solar physics have not received the credit which they deserve.

A long series of observations of Sun-spots now began, and many hypotheses of more or less ingenuity were put forward to account for the phenomena which they present. For some time, indeed, the possibility of their existence was earnestly denied by the students of Aristotelian philosophy. It is impossible, they gravely urged, that the Eye of the Universe should suffer from ophthalmia; and it is related that when Scheiner communicated his discovery of the solar spots to the provincial of his order, the latter, who was an earnest Aristotelian, answered, 'I have read Aristotle's writings from beginning to end many times, and I can assure you I have nowhere found in them anything similar to what you mention; go, therefore, my son; tranquillise yourself; be assured that what you take for spots in the Sun are the faults of your glasses or your eyes.'

Despite the defenders of Aristotle's infallibility, however, the progress of solar research went on. Galileo continued his labours, until, from viewing the Sun so often without the dark glasses now commonly employed, he lost his eyesight. Scheiner, Hevelius, and other observers, added largely to the store of known facts; and gradually the observation of solar spots began to be recognised as a regular part of the astronomer's work.

I do not propose, however, to give a detailed account of the observations made in those earlier years of telescopic observation of the Sun. Indeed, to give a full history of those observations, and to extend the

same fulness of narrative to later researches, would require twenty or thirty such volumes as the present.

I shall content myself with selecting certain illustrative instances of solar observation by the earlier astronomers, choosing those observations specially which tend to introduce the results more completely educed by recent researches.

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Cassini writes thus of a spot observed by him in August 1671. It is now about twenty years since, that astronomers have not seen any considerable spots on the Sun, though before that time, since the invention of the telescope, they have from time to time observed them. The Sun appeared all that while with an entire brightness, and I saw him so on the ninth of the month of August. But on the eleventh of the same, about six a clock at night, being furnisht only with a three-foot glass, I remarked in the Sun's disque two spots very dark, distant from his apparent centre about the third part of his semi-diameter. . . . The first of these spots, being look'd upon with a telescope of seventeen foot long, appeared of a somewhat oval figure; the other was oblong and a little curved, like the Hebrew letter Jod; and both together were surrounded by a corolla or coronet made up of little dark points' (the penumbra) which conformed itself to the figure of the spots, considered as they were joined together.... The twelfth of August, 1671, I ob

* New Observations of Spots in the Sun; made at the Royal Academy of Paris on August 11, 12, and 13, 1671; and English't out of the French. Phil. Trans. vol. vi. p. 2,251.

served them from the time of sun-rising, and perceived that they were nearer his centre. . . . The first was composed of two others almost round and conjoyn'd. The second represented the shape of a scorpion. The third was round' (this is the first intimation we have of the triplicity of the group), and they were all three environed with a coronet, which was composed, as said above, of abundance of little obscure pricks. This coronet appeared to be clearer than the rest of the Sun when looked upon with the short glass, and darker when seen with the long. Without it there were other points, 'but very black ones, viz. five near the round spot on the south side, and another near the scorpion's tail on the north side. At eight a clock and fortyeight minuts, the figure of the scorpion was seen divided into several pieces, as if his tail and arms had been cut off. The northern point remained no more, there remaining none but those seen on the south side; and the length of the enclosure of all the spots, comprehended between the extremities, was of one minut and fifteen seconds, and the breadth of thirty seconds.' On August 12 Cassini found no great change had taken place, but the black points outside the spot were now spread in a straight row. On the 13th 'the edge of the coronet was turned to a point on the south side.' The spot had indeed changed in that strange way which all observers of the Sun must be familiar with, the following extremity of the penumbra drawn out to a point which was so curled round as to be directed towards the preceding end of the spot.

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