118 ASTRONOMY AS A SCIENCE. THE SUN. 



such and so numerous have been the discoveries since 

 made. One of these, however, is the discovery of an 

 error. The mean distance of the sun from the earth 

 (calculated and accepted by astronomers upon a paral- 

 lax derived from two transits of Venus a century ago) 

 has been recently revised upon new bases of observa- 

 tion, and the estimate reduced by 3,000,000 of miles, 

 or about a thirtieth part. This correction may seem 

 trifling to those ignorant of the exactness of the science. 

 To the astronomer it is a weighty one, and the more 

 striking because derived from the concurrence of dis- 

 tinct sources of evidence. The direct proofs are from 

 astronomical observations, but one detached proof, sin- 

 gularly coinciding in date, deserves especial notice, as 

 being drawn from experiments by Foucault and Fizeau 

 on the velocity of light some of these experiments of 

 such admirable subtlety of device and execution that 

 an apparatus confined to a single room sufficed to de- 

 monstrate the velocity of a ray, passing through 185,000 

 miles in a second of time ! This rate of motion, less 

 by 7,000 miles than that deduced from the occultation 

 of Jupiter's moons, almost exactly concurs with the 

 correction just noticed as to the distance of the sun a 

 coincidence satisfying the most rigid conditions of en- 

 quiry. No fact can better illustrate the prowess of 

 modern science, in continually bringing to the dis- 

 covery of a common truth phenomena and even laws 

 seemingly distinct in the natural world. 



This remark applies not less to other polar pheno- 

 mena recently disclosed, and eminently to those great 

 discoveries by aid of the lines in the spectrum, which 



