This will appear singular, because the maximum elongation is about 27 deg., the minimum only about 18 deg..

But it happens that in our northern latitudes Mercury is always _south_ of the sun when he attains his maximum elongation, and this fact exercises a more important effect than the mere amount of elongation.] [Footnote 12: It does not seem to me that the difficulty of detecting Mercury is due to the difficulty "of identifying it amongst the surrounding stars, during the short time that it can be seen" (Hind's 'Introduction to Astronomy').

There are few stars which are comparable with Mercury in brilliancy, when seen under the same light.] [Footnote 13: I may notice another error sometimes made.

It is said that the shadow of a satellite _appears_ elliptical when near the edge of the disc.

The shadow is _in reality_ elliptical when thus situated, but _appears_ circular.