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earnest observalior. of a class of phenomena, some of which 

 could not even escape the naked eye. Simon Marius describ- 

 ed in 1612 the nebula in Andromeda, and Huygens, in 1656, 

 drew the figure of that in the stars of the sword of Orion. 

 Both nebulse might serve as types of a more or less advanced 

 condensation of nebulous cosmical matter. Marius, when he 

 compared the nebula in Andromeda to " a w^ax taper seen 

 through a semi-transparent medium," indicated very forcibly 

 the difference between nebulse generally and the stellar mass- 

 es and gi'oups in the Pleiades and in Cancer, examined by 

 Galileo. As early as the sixteenth century, Spanish and Port- 

 uguese sea-farers, without the aid of telescopic vision, had no- 

 ticed with admiration the two Magellanic clouds of light re- 

 volving round the south pole, of v/hich one, as we have observ- 

 ed, was known as " the white spot" or '• white ox" of the Per- 

 sian astronomer Abdurrahman Sufi, who lived in the middle 

 of the tenth century. Galileo, in the Kimcius Slderius, uses 

 the terms " stellcB ncbuloS(x" and " nebulosce" to designate clus- 

 ters of stars, which, as he expresses it, like areolce, sjoarsim loer 

 cEthera siibfulgent. As he did not bestow any especial atteu' 

 tion on the nebula in Andromeda, which, although visible to 

 the naked eye, had not hitherto revealed any star under the 

 highest magnifying powers, he regarded all nebulous appear 

 ances, all his Jiehulosce, and the Milky Way itself, as lumin- 

 ous masses formed of closely-compressed stars. He did not 

 distinguish between the nebula and star, as Huygens did in 

 the case of the nebulous spot of Orion. These are the feeble 

 beffinninfrs of the jrreat works on NebidcB, which have so lion- 

 orably occupied the first astronomers of our own time in both 

 hemispheres. 



Although the seventeenth century owes its principal splen 

 dor at its beginning to the sudden enlargement afforded to the 

 knowledge of the heavens, imparted by the labors of Galileo 

 and Kepler, and at its close to the advance in mathematical 

 science, due to Newton and Leibnitz, yet the greater number 

 of the physical problems which occupy us in the present day 

 likewise experienced beneficial consideration in the same cen- 

 tury. In order not to depart from the character peculiarly 

 appropriate to a history of the contemplation of the universe^ 

 ^ I limit myself to a mere enumeration of the works which have 

 exercised direct and special influence on general, or, in other 

 words, on cosmical views of nature. With reference to the 

 processes of light, heat, and magnetism, I would first name 

 Huygens Galileo, and Gilbert. While Huygens was occu- 



