RECENT EXPERIMENTS ON FOG SIGNALS. 21 1 
mental significance. There was no visible reflecting sur- 
face from which they could come. On. some days, with 
hardly a cloud in the air and hardly a ripple on the sea, 
they reached a magical intensity. As far as the sense of 
hearing could judge, they came from the body of the air 
in front of the great trumpet which produced them. The 
trumpet blasts were five seconds in duration, but long 
before the blast had ceased the echoes struck in, adding 
their strength to the primitive note of the trumpet. After 
the blast had ended the echoes continued, retreating fur- 
ther and further from the point of observation, and finally 
dying away at great distances. The echoes were perfectly 
continuous as long as the sea was clear of ships, " tapering " 
by imperceptible gradations into absolute silence. But 
when a ship happened to throw itself athwart the course 
of the sound, the echo from the broadside of the vessel was 
returned as a shock which rudely interrupted the contin- 
uity of the dying atmospheric music. 
These echoes have been ascribed to reflection from the 
crests of the sea-waves. But this hypothesis is negatived 
by the fact that the echoes were produced in great inten- 
sity and duration when no waves existed when the sea, 
in fact, was of glassy smoothness. It has been also shown 
that the direction of the echoes depended not on that of 
waves, real or assumed, but on the direction of the axis of 
the trumpet. Causing that axis to traverse an arc of 210 
degrees, and the trumpet to sound at various points of the 
arc, the echoes were always, at all events in calm weather, 
returned from that portion of the atmosphere toward which 
the trumpet was directed.' They could not, under the 
circumstances, come 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 smooth- 
ness 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. 
