THE OVERCOMING OF APPEARANCES 23 



modern i6-inch gun hurls a projectile weighing a ton, with a 

 muzzle velocity of 2000 feet per second ; yet so swift is its 

 flight that in its transit even this great mass is invisible to an 

 observer standing by. The earth, could it be weighed at its 

 own surface, would equal somewhat more than six thousand 

 million billions (6,000,000,000,000,000,000,000) of these ton pro- 

 jectiles, and it flashes through space at the rate of 100,000 feet, 

 or 19 miles per second. An express train at 70 miles an hour 

 does about 100 feet per second. 



If there were but stations along this circular railway round 

 the sun such, say, as the ancients imagined in the twelve 

 signs of the zodiac and we could take our stand upon a plat- 

 form, we should see this solitary occupant of the track pass in 

 40 seconds ; yet its greatest diameter would represent a train 

 8000 miles long. In a day its huge bulk would have dwindled 

 to the size of the moon ; in a week it would have disappeared 

 among the trackless stars. And it would not return for a 

 year. 



This strange, lone voyager of space, this planet, whirling so 

 violently upon its own axis and plunging through the sky like 

 a meteor, nothing above it, nothing below, runs its round of 

 the sun all as if it were fixed to a track, or were skimming the 

 surface of a sea. Yet as there is no track, no surface whereon 

 to run, a looker-on might think of the earth as fixed to the end 

 of an invisible arm 93,000,000 miles long, or held in leash like a 

 stone in a sling. 



Some such fanciful mechanism is just what has been imagined 

 and named Gravitation. Once it signified nothing more than 

 the primitive impression of heaviness ; it was thought of, in 

 Aristotle's time, as something real, just as was its opposite, 

 Levitation, the tendency to lightness. It is not difficult to 

 measure its effect, the force of its pull, and we know, since old 

 Sir Isaac's day, the simple formula which describes its action. 

 But when we try to conceive how across a hundred million miles 

 of seeming empty space it can hold a colossal body like the 

 earth to a rigid path, throughout long ranges of cosmic time, 

 we are baffled still. It is a world riddle. 



Seventy times round the track and the little whirl of life is 

 done. Of the first five one can remember nothing at all ; the 

 next fifteen or twenty are passed in getting accustomed to one's 



