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faint as to elude ordinary vision, and this continuity does not seem to be well established.

But there is associated with it a phenomena which is still one of the mysteries of astronomy. In the heavens, immediately opposite the sun, there is always a faint light, to which the term Gegenschein is applied. This is a German word, of which the best English equivalent is counter-glow. The light is so faint that it can be seen only under the most favourable conditions. When it falls in the Milky Way the light of that body is sufficient to drown it out, as is that of the moon, if the latter is above the horizon.

It passes through the Milky Way in June and December of each year, and can therefore not be seen during these months. Nor is it likely to be seen during the first part of January or July. At other times it must be looked for when the sun is considerably below the horizon, the sky perfectly clear and the moon not in sight. It may then be seen as an extremely faint impression of light, to which no exact outline can be assigned. The observer will find it by sweeping his eye over the region of the spot exactly opposite the sun.

There can be little doubt that the zodiacal light is caused by the reflection of the light of the sun from a swarm of very minute bodies, perhaps in the nature of meteors, continually revolving around it. We might naturally attribute the Gegenschein to the same cause, but the question would then arise why it is only seen opposite the sun. It has been suggested that possibly the earth has a tail, like a comet, and that the Gegen