PREFACE.

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Bradley. The chapter closes with an account of the most importantresults which have been elicited by the labours of successive enquirerson the subject of the Irradiation of Light.

The seventeenth chapter is devoted to the history of the physical en-quiries connected with eclipses of the Sun and Moon, the transits of theinferior planets, and other occurrences of a similar character. Thesephenomena are all influenced in so great a degree by Refraction , and theother affections of light, that it would have been inconvenient to havealluded to them at an earlier stage of the work. This chapter contains asomewhat detailed exposition of the most important facts which have beenobserved on the occasion of the various total eclipses of the Sun recordedin history, including an investigation of the conclusions which they are cal-culated to suggest respecting the physical constitution of the great centralbody of the planetary system. The subject of the transits of Venus hasnaturally suggested a brief notice of the life and labours of the lamentedHorrocks. There is a deep interest associated with the fate of this youthfulastronomer. Although dwelling in a remote district of Lancashire , inalmost entire seclusion from the rest of the scientific world, he unquestion-ably arrived at a juster appreciation of Kepler ’s discoveries than any of thesuccessors of that great astronomer had hitherto done ; while the sagacityand originality of his views on various points relating to astronomy,his fertile and glowing imagination, and his ardent enthusiasm in thepursuit of science—all seemed to foreshadow a career of uncommon bril-liancy, which a premature death unfortunately soon brought to a close.Even his brief labours, however, have assured to him a reputation whichwill live imperisliably in the annals of science. By his own countrymenhe cannot fail to be regarded with peculiar interest, as the morning starof a galaxy of men of genius, who continued for about a century to adornthese isles by their successful cultivation of the physico-mathematicalsciences. The names of Horrocks, Gascoigne, Brouncker, Barrow, Wallis,Wren, Gregory, Hooke, Newton, Taylor, Bradley, Simpson, and Maclaurin ,represent a constellation of scientific enquirers, which for splendour ofgenius and high intellectual endowments has never been surpassed, andrarely equalled, during a similar period in the history of any nation, whe-ther of ancient or modern times.

As any work relating to astronomical science would be incompletewithout some allusion to the important subject of observation, the eight-eenth chapter has been devoted to a condensed account of the pro-gress of Practical Astronomy, from the earliest ages down to the presenttime. The annals of physical science do not, perhaps, furnish a moreinteresting picture of gradual advancement towards perfection than thatwhich exhibits the successive improvements effected in this department ofastronomy—from the naked estimations of the Chaldean priests to therefined and complicated methods of observation practised by modern astro-nomers—from the gnomon and the clepsydra, in their most rudimentaryforms, to the transit circle of the Greenwich Observatory, the pendulum