IMMENSITY OF SPACE. 31 



and allow a line for each name, and then print one hundred 

 lines in a page, and make volumes of one thousand pages 

 each, and place a million volumes in a library, you would 

 require fourteen thousand such libraries to complete your 

 catalogue.' 



The portion of space we are at present acquainted with 

 is immense, and altogether beyond our powers of concep- 

 tion. A cannon-ball, moving at its usual velocity, would 

 occupy about a year in travelling from the earth to the 

 sun, or more than 200,000 years to the nearest fixed star. 

 Some of the distant heavenly bodies are so far off that 

 light, travelling at the rate of 192,000 miles in a second, 

 occupies more than 2,000 years in passing from them to 

 us ; and, for aught we know, there may exist multitudes 

 of systems of worlds immensely more distant than this ; 

 and, notwithstanding that light travels at so enormous a 

 velocity (nearly 900,000 times faster than sound), the 

 speed of gravity, according to Laplace, is at least 50 mil- 

 lion times greater. 



It has been calculated by Sir William Thomson that 

 the number of molecules in a single cubic inch of any gas 

 is about 100,000 million million millions. Each mole- 

 cule also, in different gases, consists of from two to many 

 atoms, and is believed to be continually moving to and 

 fro at a very rapid rate : in hydrogen, at about 6,055 

 feet per second, or 69 miles per minute (Joule). The 

 diameter of a particle of matter has been estimated to 

 be about -^-^ to j-J-g- millionth of an inch. According 

 to Sorby, 1 a - r ^ 5 ^th of an inch cube of liquid water 

 contains about 3,900 million million molecules. The 

 moon's influence upon the tides of the earth is about 

 21,871 ,400th part of the total influence of gravity, yet the 



1 Nature, Feb. 24, 1876, p. 333. 



