COSMOGONY JEANS 169 



size of these nebula:^, but to (ell the whole story, it must be added that 

 their colossal masses are so tenuous that each millionth part of an 

 ounce is, on the averaire, as h\g as the Matterhorn. Think of a body 

 which is bi,«:«2:er than the Matterhorn by as much as 1,0U() million suns 

 is heavier than a millionth part of an ounce, and we have the size of 

 any one of these irreat nebuhr. Any one of the three photofjraphs 

 here reproduced would have to be enlarged so as to cover the whole of 

 Asia before a body of the size of the earth became visible in it at all, 

 even under the most ]xiwerful of microscopes. 



Hubble estimates that about 2,000,000 such nebuhx^ are visible in 

 the great 100-inch telescope at Mount Wilson, and that the whole 

 universe has about a thousand million times the volume of that part 

 of space visible in this telescope. Let us now multiply 1,000 million 

 by 2 million, and the product by 1.000 million. The answer (2X 10-') 

 gives some indication of the probable number of stars in the universe ; 

 the same number of grains of sand spread over England would make 

 a layer hundreds of yards in depth. Let us reflect that our earth is 

 one millionth part of one such grain of sand, and our mundane affairs, 

 our troubles and our achievements, begin to appear in their correct 

 proportion to the universe as a whole. 



While the stars may fairly be compared to grains of sand in num- 

 ber, they differ too much inter se for the comparison to be carried 

 further. There is an enormous variety of big and little stars, of 

 briglit and faint stars, of red and blue stars, and of hot, hotter, and 

 still hotter stars. The faintest of known stars (Wolf 359) emits only 

 a fifty thousandth part of the light of the sun, while the brightest 

 (S. Doradus) emits three hundred thousand times as much light as 

 the sun. The smallest known star (Van Maanen's star) is about the 

 size of the earth ; a million such stars could be packed inside the sun 

 and leave room to spare. The largest known star (Betelgeuse) is so 

 large that 25 million suns could be packed inside it. Their ranges 

 are greater than those between a searchlight and a glowworm, or 

 between balloons and birdshot. 



Yet the stars are essentially similar structures. A normal atom 

 consists of a central nucleus round which a number of electrons re- 

 volve like planets round the sun — a miniature solar system, in fact, 

 in which the vacant space far exceeds that occupied by matter. 

 With great heat the electrons begin to break loose and fly off at a 

 tangent. The central temperatures of the stars can be calculated 

 with fair precision, and prove to be so high that most of the electrons 

 must have already broken loose from their atoms. Of recent years, 

 a great deal of labor has been devoted to testing the hypothesis that 

 practically all the electrons have so broken loose, the stripped atoms 

 and electrons flying about in a general hurly-burly like the molecules 



