474 Scientific Intelligence. [Junn, 
this appearance, the eye (which in fig. | is supposed to view the 
cloud in a direction perpendicular to the plane of the circle) must 
be so placed that the visual rays may be acutely inclined to the 
plane of the cloud; also that the cloud, if I may be allowed 
the use of an expression so awkward, must pass quite round on 
’ the other side of the moon ; that is, on the side at the greatest 
distance from the earth ; and this I hold to be impossible on 
the following grounds: Wherever there are clouds, there must 
be an atmosphere to support them. The atmosphere of the 
earth does not reach to the moon; and even allowing that it did, 
the clouds which surround this planet do not extend so far from 
its surface as the orbit of the moon is distant. The’ cloud 
observed did not exist in the atmosphere of the moon, inasmuch 
as no telescope that I ever heard of could detect such things, 
and this appearance was Aspen to the naked eye. From 
these considerations, we may, I think, infer, that the cloud did 
not exist on the further side of the moon; and, therefore, that’ 
there could be no such appearance as that described by Dr. 
Clarke. 
Let us now consider what would have been the appearance of 
the cloud, supposing it actually to encircle the moon im the 
‘direction of the horizon. The moon, as we may judge from 
Dr. Clarke’s representation, was at the full, and the iuminous 
appearance of the cloud was derived from her light. But the 
half of the moon most distant from the earth would not, in this 
situation of circumstances, have been illumined by the sun, and 
could, therefore, reflect no light on the adjacent part of the 
nebulous circle. The further half of the ring would thus not 
have been luminous ; in other words, it would have been invi- 
sible. 
I have only further to observe, that if the moon had really 
been surrounded by a circle cf cloud, and if it had been so 
viewed that the plane of the cloud produced passed through the 
eye, the appearance would have been asin fig.3. Now nothing 
is more common than to see a strait band of cloud, such as in 
Mr. Howard’s nomenclature is_called a Cirrostratus, stretching 
across the disc of the moon. Such an appearance is described 
by Dr. Clarke himself, at p. 485, where he says, that the moon 
appeared as if divided into two parts. _ We are perfectly familiar 
with such appearances in this climate, yet nobody ever supposed 
that they are caused by circles of cloud viewed in a particular 
direction. Indeed if this is the case with the Doctor, he has 
made a most unwarrantable assumption, the grounds of which 
he can best explain. If this was not the appearance of the moon, 
as viewed by Dr. Clarke, I can only account for the phenomenon 
by supposing it such as is represented by fig. 1. In either case, 
the Doctor must have taken the liberty of supposing the point of 
view altered in order to produce the appearance of Saturn, with 
a representation of which he has treated his readers in fig. 2. 
