418 — Dr. Lamont on Phenomena observed during 
a bright ring encircling the edge of the moon, and which at the 
edge itself is tolerably intense, but the intensity of which dis- 
appears very rapidly outwards. It is moreover to be remarked 
that the light may render the masses of vapour visible in different 
manners. With a certain density of the vapour, and with a certain 
intensity (always tolerably subdued) of the source of light, the 
transmitted light appears coloured reddish; with a greater den- 
sity of the vapour, the light appears white ; and when the vapour 
has attained a cloud-like density, the light becomes entirely 
stopped, the mass of vapour appearing J/ack. 
Let us now take into consideration, laying aside entirely at 
first all that relates to motion, what phenomena a mass of vapour 
between the observer and the ring of light attending a total 
solar eclipse will produce. 
First, let a portion of the moon’s edge be covered with a mass 
of vapour (fig. 3), aed; in that case the portion situated within 
the disc of the moon disappears for the observer, as does also 
that portion extending out beyond the ring of light, and there 
remains nothing but an elevation between a and 8, the height of 
which depends on the width of the luminous ring, while its 
colour is dependent on the circumstances stated above. 
Suppose we have (fig. 4) a mass of vapour, 8, a corner of 
which juts out beyond the edge of the moon, we shall then have 
a mountain-shaped prominence produced, as the figure shows. 
If we have (fig. 5) a mass of vapour, a, touching the edge of 
the moon with one corner, there will be seen at the moon’s edge 
a projection with small isolated spots. 
Let us now examine also the motion. The motion is here 
threefold. 
1. A motion of the earth on its axis, whereby the whole atmo- 
sphere, and consequently the masses of vapour suspended therein, 
are carried along over the moon’s disc from west to east. 
2. A movement of the clouds in the atmosphere, brought about 
by currents of air, whose direction, speaking in a general way, is 
not subject to any rule. 
3. A motion due to the vapour becoming dissolved or de- 
posited. 
The first of these three motions is alone regular; and its con- 
sequence would be that the masses of vapour would apparently 
become covered up by the western limb of the moon, and would, 
on the contrary, make their appearance again on the eastern 
limb. . 
With respect to the second motion, only thus much can be 
said,—namely, that it follows the course of the current of the air. 
When, therefore, the mass of vapour takes its origin in the lower 
current of air, its motion coincides with the direction of the wind; 
