292 THE POPULAR SCIENCE MONTHLY. 



of Jupiter's first satellite with the velocity of light, as determined by 

 terrestrial measurement, and so measures oflF the millions of miles be- 

 tween us and the source of almost all our energy. These four methods, 

 notably the last two, give us 92,360,000 miles as a near approximation 

 to this long-sought distance. We have thus reduced this space by 

 3,000,000 miles, or about ^*^ of the entire amount. Across this interval 

 the radiant energy of the sun dashes in eight minutes thirteen seconds. 

 Thermal electricity, which might be presumed to exist at the sun in 

 great quantity, would traverse the distance in one hour thirty-six min- 

 utes. Sensation travels along our nerves at the slow rate of about 

 150 feet a second. Imagine an infant with an arm long enough to 

 reach the sun. It would have to live 102 years to know that it had 

 burned its band in the solar fires. Counting three a second day and 

 night, it would require an entire year to count the miles intervening 

 between us and the sun ; and to count the distance in feet, at the same 

 rate, would consume 5,280 years, or nearly as much time as has elapsed 

 since the introduction of man upon the earth, according to Biblical 

 chronology. 



The sun's distance being ascertained, its absolute diameter is deter- 

 mined from the apparent by the process applied to the moon, A near 

 approximation to the sun's radius is 430,680 miles. Imagine the earth 

 at the sun's centre: its surface would appear as far distant as does 

 now the celestial vault, and the moon's orbit would fall nearly 200,000 

 miles within the surface, or little more than half-way from the centre 

 out, A locomotive at thirty miles an hour would run from centre to 

 surface in 1.63 years. Jules Verne got his traveler around the world 

 in eighty days ; at the same rate it would take him twenty-four years 

 to make the circuit of the sun. Its volume is 1,334,000 times the earth's; 

 but its mass, on account of its less density, is only 323,386 times as 

 great. "We say on/y, because the ratio of masses is so much less than 

 that of volumes. But when we reflect that the spectroscope shows at 

 least many terrestrial elements present in the sun, and that the sun 

 contains enousrh of such substantial stuff as Mother Earth consists of 

 to make more than 300,000 like her, we are prepared to admit that the 

 ratio between the masses even is large enough for all practical purposes. 



Vast and incomprehensible as we have found our distance from the 

 sun to be, we have still to contemplate far greater reaches within the 

 limits of the solar system. Juj^iter holds on its silent course 5y^Q- as far 

 away from the sun as the earth, and therefore receives only -^ the in- 

 tensity of solar radiant energy. Saturn is nearly twice as far distant 

 as Jupiter; Uranus more than twice as far as Saturn; while Neptune 

 glimmers at thirty times the earth's distance with light that has con- 

 sumed eight and a quarter hours in flashing twice across this vast 

 abyss since leaving the sun. At that distant boundary the light and 

 heat of the sun have only -^-^ the intensity that we enjoy, while its 

 apparent diameter, observed from that position, would shrink to 64", 



