thk PLANETS in octobkr. 77 
tion, however, to know about where in the celestial sphere 
this remote planet is located at the present time. It has 
recently entered the constellation Gemini and may be found 
by those who have the requisite equipment about half way 
between the stars Eta and Mu. For the majority it will 
suffice to say that it is in the Milky Way nearly midway 
between Aldebaran and Pollux. It rises on the twelfth a- 
bout half past nine, and is therefore well up from the hor¬ 
izon before midnight. 
Mercury is the nearest to the sun of all the planets, and 
so near that it is difficult to obtain a view of it unless 
the atmospheric conditions be of the best. Its maximum 
elongation being only 27 degrees, it must usually be sought 
for not more than 15 degrees from the horizon. Eet the 
observer take pencil and paper and draw a circle about two 
inches in diameter. Make a small black spot in the center 
to represent the sun and designate it by the letter N. The 
circle will represent the orbit of the planet Mercury around 
the sun. From N draw a line about three inches long and 
make a small black spot at its extremity, and letter it E. 
This line ES will represent the distance the earth is from 
the sun, and the black spot will represent it in one position 
in its orbit. Now draw a line from E so that it will just 
touch the circle but will not cut it if prolonged. Make a 
small black dot where this line and the circle touch each 
other and designate it by the letter M. This will represent 
the planet Mercury in one position in its orbit. The angle 
MES is called “ Elongation, ” or if a circle be described 
from E as a center and radius ES , the arc SM is also called 
elongation, being an arc on the celestial sphere and con¬ 
taining the same number of degrees as the angle MES. It 
will readily be seen that if the planet be in any other posi¬ 
tion in its orbit the lines EM and ES make a smaller angle 
than at position M. On the other side of the line ES there 
would be a position corresponding to M where the angle 
