Astronomical Society. '♦GS 



the first mio-hty step which pointed out a connection between spe- 

 culative Astronomy and practical utility, and which, replacing the 

 fast dissipating dreams of astrology by nobler visions, showed how 

 the stars mi^ht really and without fiction be called arbiters ol the 

 destinies of empires,— we owe to the satellites of Jupiter ; to those 

 atoms, imperceptible to the naked eye, and floating like motes in 

 the beam of their primary— itself an atom to our sight— noticed 

 only by the careless vulgar as a large star, and by the philosophers 

 of former ages as something moving among the stars— they knew not 

 what— nor why ; perhaps only to perplex the wise with fruitless 

 conjectures, and harass the weak with fears as idle as thetr theories. 

 No wonder now that the eclipses of the satellites were watched 

 with anxious, earnest interest ; they were soon to afford matter for 

 vet crreater wonder and deeper contemplation. Roemer's discovery 

 of the velocity of light from the retardation of their eclipses about 

 the end of the 17th century, was the next in order, and the subli- 

 mest truth they were destined to be the means of unfolding ; a 

 truth so amazin^', so overwhelming to human faculties, that (not to 

 mention the feebler names of Cassini, Maraldi and Fontenelle) even 

 the comprehensive genius of a Hooke quailed before it, and refused 

 to admit the existence of a motion so little short of infinite in a 

 finite system like our own. The discovery of the aberration of 

 light by Bradley, however, more than 40 years afterwards, confirmed 

 it in its full extent ; and no truth in the circle of physical science is 

 either more astonishing, or better established than this. 



We are not yet come to the end of the long catalogue of useful 

 and admirable results afforded to science and to mankind by the 

 discovery of these bodies. We have hitherto regarded only obvious 

 results • broad and evident conclusions from apparent facts. Let 

 us now'trace them in the quiet succession of their convolutions, in 

 the unfolding of their periodical inequalities, in the slowly accu- 

 mulating amount of their mutual action, in the influence of the 

 oblate figure of their primary on their orbits; m s'lort, through 

 all the mazy intricacies of their perturbations. The lessons they 

 have thus whispered to the intellect of man, over the midnight lamp, 

 have not been less instructive, less fraught with wonder and utility, 

 than those which they have blazoned to his senses. It is to that 

 powerful and gifted genius, now so recently gathered in an illustri- 

 ous grave ; on whose ashes the tears of mourning science are yet 

 warm,— to him, whose revered name so freshly sanctified by deatli, 

 I am unwilling to pronounce, that we owe the complete develop- 

 ment of their theory. His penetrating mind saw all the advantages 

 likely to accrue to the general theory of the planetary perturba- 

 tions from the study of this miniature system, where years are re- 

 presented by days, and ages by years, and where inequalities, whicli 

 in the planetary theory have a character approaching to secular, 

 can be traced in their increase and on their wane. Aided, therefore, 

 by his powerful analysis, he succeeded in applying the law of gra- 

 vitation to the minute investigation of all their mequahtics ;and the 

 result has been not merely another triumph of the Newtonian theory 

 in the complete explanation of all their complicated irregularities, 



