52 
Aprit 11. 
ORDINARY MEETING.—MR. H. PRATT, F.R.A.8., ON 
THE PHYSICAL FEATURES OF THE MOON. 
After stating that we know something of the usefulness of the 
Moon, very much of its motion, and a little about the strange markings 
on its disc, yet, to the question, ‘‘ What is its real nature ?” he affirmed 
that at present we are unable to give a positive reply. The successive 
suppositions of observers (ancient and modern) were next referred to, 
and the growth of knowledge coincident with optical improvements 
traced out. The speculations on the habitability of the moon were 
glanced at, Mr. Pratt regarding it as impossible that even vegetation 
could be the cause of the changes of lunar tints, if it were true that 
neither water nor atmosphere existed there. But those questions were 
by no means so nearly disposed of as some writers assumed. The only 
atmosphere possible to the moon must be very small.in quantity and 
limited, perhaps, in distribution, obviously increasing the difficulty of 
proving either its presence or absence. Writers of the day treated the 
subject in a most summary and inconclusive manner, yet certainly 
more delicate observations and more precise data were needed before 
it could be finally settled. Many speculations as to the locale of a 
lunar atmosphere had been made : some placed it on the farther side 
of the moon (which we never see); others had put it inside; but we 
were really not able to say what might not be inside; for as yet we 
could only deal with its exterior. 
Let us consider (said Mr Pratt) one or two points. We knew that 
the proportion of oxygen in the earth’s crust was at least one third, 
some said one half, by weight of the materials. And we knew oxygen 
united with nitrogen to form atmosphere, and combined with hydrogen 
and formed water, and with silicon, sulphur, carbon and the metals to 
form the varieties of earth and rocks which together constituted the 
solid matter of our globe. Then would it not be exceeding the bounds 
of probability to exclude oxygen from the Lunar crust? Again, here 
we knew that combustion was the process of combination between 
oxygen and other substances, Then, if volcanoes are in any way 
proof that the Lunar crust is combustible, what could we suppose 
could have taken the place of oxygen in the process? Or, if the 
Lunar crust was earthy in its nature, was it reasonable to suppose it 
