2 THE POPULAR SCIENCE MONTHLY. 



Evidently, then, no standards, which like our ordinary measures 

 bear a simple or at least a conceivable relation to the dimensions of our 

 own bodies, can help us to stretch a line in such a universe. We must 

 seek for some magnitude which is commensurate with these immensities 

 of space; and, in the wonderfully rapid motion of light, astronomy fur- 

 nishes us with a suitable standard. By the eclipses of Jupiter's sat- 

 ellites the astronomers have determined that this mysterious effluence 

 reaches us from the sun in eight minutes and a half, and therefore must 

 travel through space with the incredible velocity shall I dare to name 

 it of 186,000 miles in a second of time! Yet inconceivably rapid as 

 this motion is, capable of girdling the earth nearly eight times in a 

 single second, the very nearest of the fixed stars, a Centauri, is so remote 

 that the light by which it will be seen in the southern heavens to- 

 night, near that magnificent constellation the Southern Cross, must have 

 started on its journey three years and a half ago. But this light comes 

 from merely the threshold of the stellar universe ; and the telescope re- 

 veals to us stars so distant that, had they been blotted out of existence 

 when history began, the tidings of the event could not yet have reached 

 the earth ! 



Compare now with these grand conceptions the popular belief of 

 only a few centuries back. Where we look into the infinite depths, our 

 Puritan forefathers saw only a solid dome hemming in the earth and 

 skies, and through whose opened doors the rain descended. They 

 regarded the sun and moon merely as great luminaries set in this 

 firmament to rule the day and night, and to their understandings the 

 stars served no better purpose than the spangles which glitter on the 

 azure ceiling of many a modern church. The great work of Copernicus, 

 " De Orbium Ccelestium Revolutionibus," which was destined, ulti- 

 mately, to overthrow the crude cosmography which Christianity had 

 inherited from Judaism, was not published until just at the close of the 

 author's life in 1543, the date before mentioned. The telescope, which 

 was required to fully convince the world of its previous error, was not 

 invented until more than half a century later, and it was not until 1835 

 that Struve detected the parallax of a Lyra?. The measurement of this 

 parallax, together with Bessel's determination of the parallax of 61 

 Cygni, and Henderson's that of a Centauri, at about the same time, 

 gave us our first accurate knowledge of the distances of the fixed stars. 



To the thought I have endeavored to express I must add another, 

 before I can draw the lesson which I wish to teach. Great scientific 

 truths become popularized very slowly, and, after they have been 

 thoroughly worked out by the investigators, it is often many years 

 before they become a part of the current knowledge of mankind. It 

 was fully a century after Copernicus died, with his great volume still 

 wet from the press of Nuremburg in his hands, before the Copernican 

 theory "was generally accepted even by the learned ; and the intolerant 

 spirit with which this work was received, and the persecution which 



