16 WHAT IS LIFE ? 



and year the standard by which we are measuring the 

 time of the motion of other bodies. 



Mars, the next planet, has a day of about twenty- 

 four and a half hours of our terrestrial time, and its 

 year is about 687 days. 



Jupiter, the next planet to Mars, has a day of nearly 

 ten hours of our terrestrial time, and its year is about 

 4333 days. This planet has five moons, visible ; each 

 differs in its time of revolution round Jupiter. 



Saturn, with its wonderful rings, an object apparently 

 unique in the heavens, has a day of about ten hours 

 terrestrial time, but Saturn's year is about 10,759 

 days. 



So also has Uranus a day (probably about nine and 

 a half hours), but its year consists of about 30,687 

 clays. 



Neptune also has its special day and year of 60,127 

 clays. 



Smaller masses of matter, minor planets, their number 

 unknown, each one has its specific day and year. 1 



1 " There seems to be a regular gradation of size, therefore, ranging 

 from Sirius to dust ; and apparently we must regard all space as full 

 of these cosmic particles stray fragments, as it were, perhaps of 

 .some older world, perhaps going to help to form a new one some day." 

 (" Pioneers of Science," Prof. 0. Lodge, F.R.S., 1893, p. 332.) 



"There appears to be no special size suited to the vastness of 

 space ; we find, as a matter of fact, bodies of all manner of sizes, 

 ranging by gradations from the most tremendous sans, like Sirius, 

 down through ordinary suns to smaller ones, then to planets of all 

 sizes, satellites still smaller, then the asteroids, till we come to the 

 smallest satellite of Mars, only about ten miles in diameter, and 

 weighing over some billion tons the smallest of the regular bodies 

 belonging to the solar system known." (Idem, p. 331.) 



" Between our solar system and these other suns between each of 



