There was considerable difficulty in selecting a proper title for this paper. It may appear to some, after reading it, that a shorter and better title would have been, “On the Hazing Effects of Smoke.” But as smoke particles generally reflect a reddish-brown light, they do not therefore seem to be the cause of the whitish light which we call haze; and further, smoke particles generally condense into little masses of such a size that they fall to the ground before they are carried to any great distance. It was thought that as this paper is a continuation of previous work, and is founded on results already communicated to this Society, it would be better to keep to the use of the same terms, and as usual, under the name of “dust particles,” to include all the solid and liquid products of combustion, of whatever size or colour they may be.