ASTRONOMICAL DISCOX ERIB3. t51 



of Columbus) in respect to our knowledge of terrestrial space. 

 It not only infinitely extended our insight into creation, but 

 also, besides enriching the sphere of human ideas, raised 

 mathematical science to a previously unattained splendor, 

 by the exposition of new and complicated problems. Thus 

 the increased power of the organs of perception reacts on 

 the world of thought, to the strengthening of intellectual 

 force, and the ennoblement of humanity. To the telescope 

 alone we owe the discovery, in less than two and a half 

 centuries, of thirteen new planets, of four satellite-systems 

 (the four moons of Jupiter, eight satellites of Saturn, four, 

 or perhaps six of Uranus, and one of Neptune), of the sun's 

 spots and faculse, the phases of Venus, the form and height 

 of the lunar mountains, the wintery polar zones of Mars, the 

 belts of Jupiter and Saturn, the rings of the latter, the inte- 

 rior planetary comets of short periods of revolution, together 

 with many other phenomena which likewise escape the na- 

 ked eye. While our own solar system, which so long seemed 

 limited to six planets and one moon, has been enriched in 

 the space of 240 years with the discoveries to which we 

 have alluded, our knowledge regarding successive strata of 

 the region of the fixed stars has unexpectedly been still more 

 increased. Thousands of nebulae, stellar swarms, and double 

 stars, have been observed. The changing position of the 

 double stars which revolve round one common center of 

 gravity has proved, like the proper motion of all fixed starb, 

 that forces of gravitation are operating in those distant re- 

 gions of space, as in our own limited mutually-disturbing 

 planetary spheres. Since Morin and Gascoigne (not indeed 

 till twenty-five or thirty years after the invention of the tel- 

 escope) combined optical arrangements with measuring in- 

 struments, we have been enabled to obtain more accurate 

 observations of the change of position of the stars. By this 

 means we are enabled to calculate, with the greatest pre- 

 cision, every change in the position of the planetary bodies, 

 the ellipses of aberration of the fixed stars and their paral- 

 laxes, and to measure the relative distances of the double 

 stars even when amounting to only a few tenths of a sec- 

 onds-arc. The astronomical knowledge of the solar system 

 has gradually extended to that of a system of the universe. 

 We know that Galileo made his discoveries of Jupiter's 

 satellites with an instrument that magnified only seven diam- 

 eters, and that he never could have used one of a higher 

 power than thirty-two. One hundred and seventy years later, 



