When I communicated my first note on this subject on the 21st of January last, the only definite conclusion I had then arrived at was that the very remarkable and brilliant colour effects, lately seen in the heavens at sunrise and sunset, were due to the presence of an unusual amount of dust at the time floating in our atmosphere.This atmospheric dust acts as a sifting medium, breaks up the white light into its components, and reflects all the different colours to us from different parts of the sky.