Clue: Mirror supplies base to support Independent publication (5)
Answer: IMAGE
Explanation: Definition: Mirror
 E(in maths, an abstract number that is the base for natural logarithms) **placed below**(to support, in a down clue) [ I(abbrev. for "Independent", a non-member of any political party) + MAG(short for "magazine", a periodical publication) ].
Defn: …/a thing regarded as an accurate representation of something else, as in "the eyes are the mirror of the soul".