ASTRONOMICAL MAGNITUDES AND DISTANCES. 293 



or little more than the greatest apparent diameter of Venus. We 

 modestly lay claim to this small corner of the universe, denominated 

 the solar system, and assert our right to possession by calling it ours. 

 What is the area of this plane bounded by Neptune's orbit, with which 

 the planes of the other planetary orbits nearly coincide ? What is the 

 space swept by the radius-vector of this planetary child of Adams's 

 and Le Verrier's calculations ? Since circles are as the squares of their 

 radii, this area is 900 times that comprised within the earth's orbit. 

 Breaking this unit up into smaller ones, we find it contains twenty-six 

 billions, five hundred millions of millions of square miles ; or, with ref- 

 erence to the earth's entire surface, the ratio between it and the area of 

 its orbit is 13,520,000. But Neptune's orbit exceeds this 900 times ! 



Conceive this orbit immersed in the universal ether, like an immense 

 ring mapped out on the surface of still water. A pebble dropped at 

 the centre of this ring would send its widening wavelets outward with 

 a perfectly definite velocity. So a wave of light, emanating from the 

 sun, with a length of no more than the jl-fg- part of an inch, is propa- 

 gated through this universal ether with such rapidit}' that in four hours 

 and nine minutes it describes the entire area comprised wdthin Nep- 

 tune's path around the sun. 



Across this vast interval quivers, too, in some mj-sterious way, that 

 universal influence that we call gravitation. But at that outlying point, 

 where Neptune holds on its silent course, it no longer exercises that 

 dominant sway that characterizes it at the earth. The earth moves 

 through 18.4 miles of its orbit every second, and is deflected from a 

 straight line by the sun during that interval a little less than -^^^ of 

 an inch (0.11598 inch), Neptune travels 3.35 miles a second, and is 

 deflected from a straight line during the same time only about ^q^^q q - 

 of an inch (0.000129 inch) ; yet by that slight pull the sun asserts its 

 mastery, and brings Neptune round once in 164 years. 



Vast as is this field of solar operations, we demand a still broader 

 sphere for the exercise of our intellectual faculties. The successive 

 eminences on which Astronomy has planted her appliances for more ad- 

 vanced operations stand related to each other as the terms, not of an 

 arithmetical, but of a geometrical progression. Having settled the rela- 

 tive distances of this rather unsocial family of planets, the next advance 

 is on to the stars. From the measurement of a base-line a few miles in 

 extent, the astronomer essaj's, with undaunted hardihood, to fathom by 

 triangulation the depths of space. The dog baj'S at the moon, the child 

 stretches out its tiny hand to pluck the stars from the sky, and the as- 

 tronomer applies his measuring-rod along the vibrating lines of light 

 so far into immensity that blazing suns, exceeding in brightness the 

 mid-day splendor of our own, dwindle to the luminous points of twin- 

 kling stars. 



When Copernicus, the Polish astronomer, sought to extricate as- 

 tronomy from the hopeless complexity into which it had become en- 



