1919 .] 
Astronomical Notes. 
193 
ASTRONOMICAL NOTES. 
Description of a Planisphere. 
The planisphere is an instrument which shows in projection the visible 
celestial hemisphere at any hour during the year. It consists of the 
following parts :— 
A. The Star-chart (fig. 1).—This consists of a disc containing a polar 
projection of the celestial sphere extending to polar distance 180° — </>, where 
0 is the latitude for which the instrument is constructed. The particular 
planisphere which is here described is constructed for latitude 40° S., and 
therefore the polar projection extends from the South Pole to declination 
50° N. The disc bears on its margin a graduated circle A x with dates 
from March 21/22 at R.A. xxiv uniformly counter-clockwise ; the R.A. 
which stands opposite each day thus represents the sidereal time at mean 
noon (Greenwich). 
B. The Longitude Circle. — This consists of a ring containing two 
graduated circles (the two outermost circles in fig. 2); the outer circle B x 
L6—Science. 
