PREFACE.

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clock of the most improved construction, and the electro-magnetic record-ing apparatus of the American astronomers.

In this chapter I have given a somewhat detailed account of the RoyalObservatory of Greenwich , from its origin down to the present time. Theobservations which have emanated from that noble establishment haveproved of incalculable service to astronomical science. No other similarinstitution, whether of ancient or modern times, can compare with it inthis respect. Its history affords an instructive lesson regarding the ad-vantage to he derived from applying the resources of an observatory tosome definite object, and maintaining that object in view with unswervingconstancy of purpose. An uninterrupted succession of eminent astro-nomers, who have directed the labours of this establishment, have con-tributed to render it the storehouse from which the materials for deter-mining the elements of Astronomical Science have been mainly derivedin modern times. With the triumphs of the Theory of Gravitation itshistory is inseparably associated. During the early period of its exist-ence, it had the glory of supplying Newton with a series of observations,which served as a valuable guide to him while engaged in threading hisway through the intricacies of the lunar theory, and it has continued eversince to furnish almost exclusively the astronomical facts, by an appeal towhich the successors of that illustrious geometer have been enabled toestablish the accuracy of their theoretical results. The recent reductionof the entire mass of the Greenwich Observations of the Moon and Pla­ nets , extending from 1750 to 1830, under the superintendence of thepresent Astronomer Roj r al, is an achievement which, while in respect ofvastness it has few parallels in the annals of science, at the same timeforms one of the most valuable acquisitions which Astronomy has receivedduring the present century.

As a fitting sequel to the subject above-mentioned, the nineteenth chap-ter contains a brief account of the labours of astronomers in the con-struction of Catalogues of Stars. It is impossible to exaggerate theimportance of this department of Astronomical Science. The places ofthe stars constitute so many fundamental facts, upon which depend allexact conclusions relative to the movements of the planetary bodies.The labours connected with their determination afford ample scope fortalents of the highest order; but it must be acknowledged that they offerlittle to captivate either the imagination or the intellect, while at thesame time they demand the most arduous exercise of the attention, andthe most unflinching perseverance. Despite these disadvantages, therehave not been wanting numerous examples of astronomers who, disre-garding the eclat which usually attends discovery, have devoted the bestportion of their lives to the construction of a Catalogue of Stars. La-caille, Piazzi, and Groombridge will be especially remembered in theannals of astronomy, as individuals who sacrificed their days and nightswith unwearied assiduity to this object, cheered only by the consciousnessof the advantages which posterity would derive from their labours, and