AND DISTANCE FROM THE EARTH 



Gilbert's Ferdinando said on another occasion, '* we know it's 

 very clever, but we do not understand it," let us endeavor 

 to convey a clear impression of this minute angular value of 

 the solar parallax, amounting to less than nine seconds of 

 arc, and to determine which astronomers have spent so 

 many years of diligent research aided by every known 

 optical device. How much, then, does a second of arc 

 represent ? Of course the unaided eye is totally incapable 

 of estimating it Prof. Pritchard, wliose rtsearches on 

 stellar parallax have made him famous, says: "It will 

 couve}' l)Ut little idea if we say it is the 324-thousandth of 

 a right angle, for the very numbers confuse the mind. 

 But what then is a second? It is equivalent to the angle 

 subtended by a ring one inch in diameter, viewed at the 

 distance of three miles and a third. The correction to be 

 made to the sun's parallax is just one-third of this ; that is 

 to say, it is the error which a rifleman would make who shot 

 at the right-hand edge of a sovereign placed twelve miles 

 off, and who hit it by mischance just on the left edge ! It 

 is what a human hair would appear to be, if viewed at the 

 distance of over 150 feet ! " 



Yet we kiK)w the distance of the sun far within the 

 limits of the proportion above indicated, and if the second 

 of arc is such a small quantity, what then must be the 

 labours of our astronomers who deal wnth a sub-division 

 again of the second referred to, into one hundred parts, 

 each of which division represents 100,000 miles in the 

 determination of the sun's distance. 



The last two transits of 1874 and 1882 were very suc- 

 cessfully observed by astronomers of every nationalit5\ and 

 aided by photography, which played such an important 

 part on these occasions, the results liave confirmed the fact 

 that the sun's parallax was smaller than hitherto estab- 

 lished. From a combination of the results of both transits, 

 Prof. Newconibe deduces a parallax of 8.776" correspond- 

 ing to 92,350,000 miles. 



