50 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



Reduction 

 of observa- 

 tions long 

 neglected. 



(221.) 

 Bessel his 

 early la- 

 bours. 



(222.) 

 His Funda- 

 menta As- 

 tronomice : 



pause. Until very recent times, with few exceptions, 

 our observers, however industrious, have merely 

 used mechanically the apparatus put into their hands 

 by intelligent and conscientious artists, who yet, 

 never having occasion to apply their own handiwork 

 to the purposes for which it was made, could not be 

 expected to detect deficiencies of construction, nor 

 to possess the mathematical knowledge required to 

 remedy them. To determine in a complete and inde- 

 pendent manner the errors, not only of adjustment, 

 but also of construction of the instruments, and to 

 correct them by calculations (deduced when neces- 

 sary from frequent observations of their amount) is 

 now felt to be the duty of the astronomer himself. 

 This improvement (though, as we shall see, already 

 partially practised even in England) was mainly due 

 to Bessel, whose name we have placed first at the head 

 of this section. But astronomy owes to him much 

 more than this. He first showed that it is part of 

 an intelligent astronomer's duty, not only to observe 

 stars and planets, but to undergo the vastly greater 

 labour of comparing his results with the best theories 

 of his time, and of improving as far as possible those 

 theories, so as to hand over each branch of science to 

 his successor in a more perfect state than that in 

 which he found it. In all these respects practical 

 astronomy commenced a new epoch in Germany, and 

 on this account principally we place the name of 

 Bessel in a conspicuous rank. 



FRIEDRICH WILHELM BESSEL was born at Minden 

 on the 22d July 1784. He was destined for a mer- 

 cantile career ; and it is an interesting fact that it was 

 the expectation of an appointment as supercargo on 

 a commercial voyage which led him to study naviga- 

 tion and astronomy, and finally induced him to de- 

 vote his entire energies to the latter science, in which 

 he received every encouragement from the amiable 01- 

 bers, who fortunately inhabited Bremen, where young 

 Bessel was engaged in business. He commenced his 

 astronomical career by reducing Harriott's observa- 

 tions of the comet of 1607, and was thereafter ap- 

 pointed assistant to Schroter at the observatory of 

 Lilienthal . In 1 8 1 he was removed by the Prussian 

 government to the charge of the observatory about to 

 be erected at Kb'nigsberg, where he spent the re- 

 mainder of his life, and which he very speedily raised 

 by his labours to almost the first rank of European 

 observatories. In fact, he possessed, in a singular 

 degree, the qualifications for directing a great obser- 

 vatory ; including a thorough acquaintance with the 

 use of instruments, with the theory of astronomy in 

 all its branches, with the higher mathematics, and also 

 the art and practice of calculation, as well as with 

 many allied branches of natural philosophy. 



The work by which he is perhaps best known, the 

 Fundamenta Astronomies, is not grounded on his own 

 observations, nor even those made in the same cen- 

 tury, nor in his own country, but, what may appear 

 singular, upon the observations of Bradley at Green- 



cti 



wich in 1750 and some following years. In reality, reduc- 

 no better observations had been then made. The in- ilon of 

 struments had undergone no material change during / a e ^ 

 the long and industrious, though not splendid, career tions. 

 of Maskelyne ; and Bradley was beyond question the 

 most accomplished astronomer of the 18th century. 

 Let us record it as a fact for the encouragement of 

 conscientious labour in the service of science, that 

 these precious records of the state of the heavens, of 

 which the value seemed unknown to a whole succeed- 

 ing generation (so that they were not even printed 

 in a crude form until nearly fifty years after they 

 were made), were disintei-red, so to speak, by an 

 illustrious foreigner, and in course of time made the 

 basis of what, in respect of precision and method, 

 might be called a new astronomy. Bessel was as- 

 sisted in this work by a grant from the British Board 

 of Longitude. 



The observations especially considered by Bessel (223.) 

 are those of the fixed stars. To apprehend their im- s P ecial ' 



* * :*. *& *i 



portance, we must recollect that the foundation of 

 accurate knowledge of the orbits, and of the pertur- 

 bations of the Solar System, not to mention less ap- 

 parent but not less remarkable changes of place in 

 the stars themselves, consists in rendering perfectly 

 comparable observations of position at one time with 

 those made at another more or less remote. Now, 

 not only are our transit instruments and quadrants, 

 and circles, and clocks, affected with errors more 

 or less unknown, so that the registered figures re- 

 quire correction ; but, in consequence of Refraction 

 and Aberration, we see no body whatever exterior 

 to the earth in its real visual position ; and this 

 visual position, when found, is affected by Parallax. 

 Besides all this, the grand points of reference in 

 the sky, the Pole and the line of Equinoxes, are 

 undergoing perpetual, though small, changes of po- 

 sition : the first star of Aries had already, in the 

 time of Hipparchus, wandered from the point of in- 

 tersection of the Equator andEcliptic; consequently, 

 longitudes and right ascensions have to be reckoned 

 from a directional line in space altogether imaginary. 

 The pole of the heavens wanders amongst the stars, in 

 consequence of Nutation the obliquity of the Ecliptic 

 is itself changing; and, to crown all these causes of per- 

 turbation and seeming unsteadiness, the stars called 

 fixed have (as we have formerly seen) peculiar and 

 individual displacements not accounted for by any of 

 the preceding causes of change. ' In short, nothing is 

 fixed and comparable, except our measure of time. 

 The length of the sidereal day is subject to no secular 

 variation. The bases of Astronomy, the Funda- 

 menta Astronomice, then, evidently consist in the 

 perfect evaluation of all these varying elements, so 

 that the stars, if not really fixed, may become, for us 

 at least, virtually so, that by their aid the position 

 of" the fundamental directional lines of the sphere 

 may at any time be found, and the relative positions 

 of the stars themselves. After this it is easy to 



