248 



REPORTS ON THE STATE OF SCIENCE. 



the constellation Orion itself. In some cases at least, in Orion and the 

 Pleiades, they are set in a diffused nebulosity of enormous extent. 



Another phenomenon associated with spectral type, of which these 

 Orion stars show the extreme case, is perhaps the strangest result of 

 all. Astrophysicists have arranged stars by their spectra, in what 

 they believe to be the successive stages of evolution. Now it has been 

 recently found that stars of an early type of spectrum, that is in an early 

 stage of evolution, have much slower individual motions than those in 

 a later stage. It seems as though a star is born with no motion at all 

 and gradually acquires or grows one. 



This concludes my first rapid survey of the subject and we must 

 now look at some of the details more closely. In considering the dis- 

 tribution of the stars we may very well begin by taking those in our 

 own immediate neighbourhood. We will start from the sun as centre 

 and take a sphere ninety-five billion miles in radius, roughly a million 

 times the radius of the earth's orbit. This will contain what is probably 

 a normal though rather a small sample of the stars. The table, for 

 which I am indebted to the Astronomer-Eoyal, gives all the stars known 

 to be inside that sphere; they are seventeen in number, or eighteen 

 counting the sun. 



The Seventeen Nearest Stars. 

 (Stars distant less than 95,000,000,000,000 miles from the sun.) 



There may be a few others that have not yet been found, but I 

 think it is unlikely that more than two or three have escaped detection, 

 unless they are bodies of very feeble luminosity. Of course, we cannot 

 base extensive generalisations on so small a table, but I shall use it to 

 illustrate conclusions which are in reality based on more elaborate 

 researches. First, it gives a measure of how tightly the stars are 

 packed. Think of a globe of space whose circumference is the earth's 

 orbit, then think of a volume a million million million times greater; 



