HISTORY OF PHYSICAL ASTRONOMY.

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apart from these considerations, the difficulty of pointing truly to a Gelestialbody an instrument furnished for that purpose merely with pinnules, pre-sented an insuperable obstacle to the attainment of a high degree of preci-sion in the ascertainment of its apparent position. This was a constantsource of error which the astronomer had to contend with in all hisoperations, w r hose vitiating influence was essentially beyond the reacheither of the ingenuity of the mechanician or the skill of the artist. Itis to be remarked, however, in favour of the Tychonic school of observa-tion, that it served effectually to demolish the whole of the ancient fabricof epicycles, and to establish the elliptic theory of the planets upon anincontrovertible basis. This was unquestionably a noble triumph ofgenius and practical skill; but in so far as regards the more delicatephenomena of the celestial regions, the methods practised in that schoolwere utterly powerless. The sublime theory of planetary perturbationwould have proved a subject of barren research to Newton and hissuccessors, and those minute movements of the stars, in connexion withwhich so many brilliant triumphs have been achieved in recent times,would have for ever continued to be involved in impenetrable mystery,unless a complete revolution had been effected in the condition of prac-tical astronomy as it existed about the middle of the seventeenthcentury.

The establishment of public observatories in several countries ofEurope about the time referred to, could not fail to exercise a directinfluence of a favourable character upon the progress of astronomy in allits branches. When it is considered that the various movements of thecelestial bodies require for their development a series of cycles of time,many of which are of long duration, it is manifestly indispensable, in orderto arrive at an accurate knowledge of the laws of their movements, thatthe various bodies should be made the objects of continuous observationthroughout a long succession of ages. But, on the other hand, it is notless obvious that the limited resources of private individuals areinadequate to a task of such magnitude. Much, indeed, may be effectedby genius and perseverance, as in the case of Hipparchus , and severalastronomers of modern times; but, generally speaking, it is only by thesteady application of national resources to the observation of the celestialbodies, that a series of foots can be established which shall possess suffi-cient value to form a sure groundwork for the investigation of the law r s oftheir movements. The earliest public observatory, and indeed the onlyone which history makes mention of as having existed in ancient times,was that which Ptolemy Soter established at Alexandria, and which con-tinued for many centuries to furnish an asylum to the Greek astronomersin the midst of a declining civilisation. The magnificent establishmentwhich Frederick III., of Denmark, assigned to Tycho Brahe , in theisland of Huena, for the purpose of enabling him to prosecute his laboursmore effectually, cannot be called a public observatory, since it was notdesigned to promote any ulterior object connected with astronomy. Butindeed, even in so for as Tycho Brahe himself was concerned, it was soonapparent, from the disgraceful treatment which he experienced in thelatter period of his life, that the establishment of Uranibourg was heldby a very precarious tenure. It would seem, however, that Christian IV. ,under whose minority Tycho Brahe was compelled to abandon his nativecountry, felt a disposition to make some reparation for his early indif-ference to the cause of science, by the establishment of a public obscr-