196 
junction with the sun so that the comet is then at a great distance 
from the earth and its place in the heavens is moreover not far from 
the sun. The circumstances are more favourable at the opposition in 
1912, although the comet then remains invisible for our northern 
regions owing to its considerable southern declination. In order to 
calculate an ephemeris for that opposition I have first derived the 
following expressions for the heliocentric co ordinates : 
v = [9.99 3799] sin w + 77°42'18".3) 
y = [9.87 6101] sin w — 20 52 48 .5) 
z = [9.83 2770] sin (v 1 43:55<.6) 
The rectangular solar co-ordinates have been taken from the 
Nautical Almanac and reduced to the mean aequinox of the beginning 
of the year. 
The resulting mean places of the comet were reduced to the 
aequinox of the date by means of the constants f, g, G of the 
Naut. Alm. 
The following table gives the apparent places of the comet for 
Greenwich mean noon; column M gives the theoretical brightness 
1 
according to M=. It may be remembered, that the value of 1 
ro 
for the time of the photographs by Worr in 1906 varied between 
0.032 and 0.038. 
