HISTORY OF PHYSICAL ASTRONOMY.

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shew that he observed the spots as early as the month of April, 1611.On some day in that month he announced the existence of the solar spotsat a conference of savans, held in the garden of Cardinal Bandini atRome . This fact was afterwards adduced in support of his claims to theoriginal discovery of the phenomena, and was corroborated by severalpersons who were present at the conference. A fourth individual to whomthe discovery of the solar spots has been attributed is Hariot , the cele-brated mathematician of England. De Zach, who visited this countrytowards the close of the last century, obtained access to the manuscripts ofHariot , and from an inspection of them he came to the conclusion that theauthor had observed the solar spots as early as the month of December,1610. The late Professor Rigaud, of Oxford, however, having carefullyexamined the same manuscripts, found that the observations contained inthem could not bear the interpretation put upon them by De Zach. Itturns out, in fact, from his researches, that Hariot did not commence hisobservations of the spots before the month of December, 1611. Withrespect to the other three individuals whose names are associated with thediscovery of the phenomena, it is pretty evident that the claims of two atleast are well founded. Fabricius and Galileo appear to have both per-ceived the spots about the same time. The observations of Schemer wereof a later date, but it is not impossible that they may have been quiteindependent of those of his contemporaries.

The discovery of the solar spots soon conducted astronomers to theimportant conclusion that the sun has a rotatory motion round a fixedaxis. Fabricius found that all the spots had a common motion on thesun’s disk from east to west. Their motion was greatest when they werein the centre of the disk, and it thence gradually diminished until theyreached the western limb, when they disappeared from observation. Inthe course of ten days afterwards the spots reappeared on the easternlimb. Their motion at first was slow, but it continually increased untilthey reached the centre of the disk, when it again attained its maximumrate. He also found that the magnitude of the spots appeared to begreatest when they were on the centre of the disk, and least when theywere near either of the limbs. He remarked, that according to theprinciples of perspective, all these appearances -would ensue on the sup-position that the spots were attached to the surface of the sun, the latterbeing supposed at the same time to revolve round an axis with a uniformmotion from east to west. He does not appear, however, to have formedan adequate conception of the importance of this conclusion, for he did notpursue any further researches in connexion with it.

Galileo reasoned on the subject with his usual sagacity. The variouscircumstances connected with the phenomena of the spots soon revealed

vations. Qui aurait ose concevoir des doutes sur la sincerite d’une declaration de Galileecon 9 ue en ces terms: Tel jour, en 1611, je vis une tache pres du bord oriental du Soleil;tel autre jour elle etait au centre du disque; a telle troisieme date je fus temoin deladisparition de la tache derriere le bord occidental ? On trouve des observations de cegenre dans les lettres que l’illustre physicien ecrivit a Welser d’Ausbourg, mais elles sonttoutes des mois d’Avril et de Mai, 1612.” ( Annuaire , 1842, p. 469.) From the abovepassage we infer that if M. Arago had been acquainted with Mr. Airy’s “ HistoricalStatement of Circumstances connected with the Discovery of the Planet exterior to Uranus ”at the time when he was engaged in drawing up the critical remarks on that subject, whichappeared in the C omptes Rendus for the 19th October, 1846, he would have concededsubstantially to Mr. Adams his right to the discovery of the Trans-Uranian planet, as un-hesitatingly as in the present instance he concedes hypothetically to Galileo his right tothe discovery of the solar spots.