e from the glassy sea; while both their
variation of direction and their perfectly continuous fall into
silence, are irreconcilable with the notion that they came from fixed
objects on the land. They came from that portion of the atmosphere
into which the trumpet poured its maximum sound, and fell in intensity
as the direct sound penetrated to greater atmospheric distances.

The day on which our latest observations were made was particularly
fine. Before reaching Dungeness, the smoothness of the sea and the
serenity of the air caused me to test the echoing power of the
atmosphere. A single ship lay about half a mile distant between us
and the land. The result of the proposed experiment was clearly
foreseen. It was this. The rocket being sent up, it exploded at a
great height; the echoes retreated in their usual fashion, becoming
less and less intense as the distances of the invisible surfaces of
reflection from the observers increased. About five seconds after the
explosion, a single loud shock was sent back to us from the side of
the vessel lying between us and the land. Obliterated for a moment by
this more intense echo the aerial reverberation continued its retreat,
dying away into silence in two or three seconds afterwards. [Footnote:
The echoes of the gun fired on shore this day were very brief; those
of the 12-oz. gun-cotton rocket were 12" and those of the 8-oz.
cotton-powder rocket 11" in duration.]

I have referred to the firing of an 8-oz. rocket from the deck of the
'Galatea' on March 8, 1877, stating the duration of its echoes to be
seven seconds. Mr. Prentice, who was present at the time, assured me
that in his experiments similar echoes had been frequently heard of
more than twice this duration. The ranges of his sounds alone would
render this result in the highest degree probable.

To attempt to interpret an experiment which I have not had an
opportunity of repeating, is an operation of some risk; and it is not
without a consciousness of this that I refer here to a result
announced by Professor Joseph Henry, which he considers adverse to the
notion of aerial echoes. He took the trouble to point the trumpet of
a syren towards the zenith, and found that when the syren was sounded
no echo was returned. Now the reflecting surfaces which give rise to
these echoes are for the most part due to differences of temperature
between sea and air. If, through any cause, the air above be chilled,
we have