468 Dr. G. Johnstone Stoney : Survey of that part of 



Group A {Stellar Distances) . 



The last group is that of stellar distances. These are most 

 conveniently measured in metro-sixteens. 



The four units we have found it most convenient to use in 

 dealing with large magnitudes are very simply related to one 

 another, as appears from the following list of them. 



The unit we have found it convenient to use for geographical 

 distances is the stage, the stage being a million of centimetres, 

 or ten kilems, or 6j miles. 



The unit for the distances of satellites from their primaries 

 is the Earth quadrant, the quadrant being 1000 stages. 



The unit for the distances of planets from the Sun is the 

 metro-ten, the metro-ten being 1000 quadrants, which is the 

 same as a million stages. 



The unit for stellar distances is the metro-sixteen, the metro- 

 sixteen being a million metro-tens, or one billion stages. 



The position which the metro-sixteen, or billion stages, 

 occupies is indicated on the table. Light in the open aether 

 takes 1'056 year (nearly a year and three weeks) to travel a 

 metro-sixteen, so that the metro-sixteen is a little more than 

 what, in astronomy, has sometimes been called the " light- 

 year. 



The distances of the nearest stars, those few of which the 

 parallax can be directly measured *, fall within Aw, the sub- 

 section of smallest stellar distances, as appears from the 

 examples shown in fig. 5. 



Thus Aiv includes the distances of the ■ nearest stars along 

 with sub-stellar distances, that is, distances from the Sun to 

 stations between the solar system and the nearest star. Such 

 sub-stellar intervals probably exist between the stars of a 

 cluster. 



The farthest stars visible to us are probably less than 

 10,000 times farther than the few whose parallax can be 

 directly measured, since a star sending us one hundred- 

 millionth part of the light of Sirius would probably not 

 be visible. 



If this view is correct, At', which is the middle sub-section 

 of Group A, provides places to represent the distances of the 

 stars visible to the naked eye, along with all those which our 

 telescopes can reach. Accordingly, a sphere of which the 

 radius is a metro-twenty, or some two or three metro-twenties, 

 would include our whole stellar universe. Now our table 

 extends 1000 times beyond the column of metro-twenties ; so 

 that the greater part of sub-section Au makes provision for 

 measuring distances as much farther out than the most 

 distant star known to us, as a sphere with a mile for its radius 

 * See footnote on p. 46.2. 



