Jfatttre's Operations which Man is competent to Study. 407 



order of magnitude. This appears from fig. 3, in which the 

 distances may conveniently be expressed as so many Earth- 

 quadrants, meaning by the "quadrant" 1000 stages, or 

 10,000 kllems, which is approximately the distance on the 

 Earth's surface from the Equator to the Pole. 



There remains the w sub-section, the sub-section of smallest 

 Planetary measures. These stand related to the other Planetary 

 distances in somewhat the same way as Microscopical intervals 

 are related to other laboratory measures. They may be called 

 Geographical intervals, since in this sub-section we measure the 

 radii of the planets and distances on their surfaces : quantities 

 which can conveniently be expressed as so many stages, each 

 stage being ten kllems (or G| miles *), as shown in tig. 4. 



Fig. 4. 

 Radii of Planets, expressed 



in stages. 



The Sub-section Bw provides 



for all of these.J 



Gkoup E. 

 Planetary Intervals. 



Bw 



ooo ooo ooo 



Fig. 5. 



Examples of Measured Stellar 



Distances, expressed in 



metro-sixteens. 



[The Sub-section Aw provides 



for all of these.] 



Earth-quad- ) i ]_ 

 rant, j i 



1 



ooo 





E Sun! ° f }'*>$ 750 





Eadii of 









Mercury, j 



240 







Venus, 



610 







Earth, 



637 







Mars, 



340 







Jupiter, 7 000 







Saturn, 6 100 



' 





Uranus, 2 500 







Neptune, 2 GOO 





Group A. 

 Stellar Distances. 



Aw 



I) 000 000 ooo 



One Metro-sixteen, ■ 

 Distance at which par- 

 allax would be 1", 



Distances of 



a Centauri . . j 

 61Cygni ....j 



Sirius i 



a Lyrse 1 



}8-l 



Limit of distance ~\ 

 that can be l o a 

 ascertained by ( 

 parallax J 



* That is, 6^ metric miles. In Science the mile of 1600 metres, the 

 furlong of 200 metres, the chain of 20 metres, and the perch or pole 

 of 5 metres, should always be used instead of the so-called " imperial " 

 measures of the same names. Here the old or imperial measures are to 

 the new or metric measures in the ratio of 100582 to 100, which is the 

 same as the ratio of 172-8 to 171-8, between which last numbers the 

 difference is 1. 



2K2 



