218 
PROFESSOR TYNDALL ON THE ATMOSPHERE 
sounds. Returned and recovered faint sounds at the buoy. Fog cleared at 10.15 and 
instruments ceased.” 
On Saturday morning, February 7, a very dense fog prevailed, apparently thicker at 
sea than on land ; but on shore objects were invisible at between fifty and a hundred 
yards distance. 
“At 8.15 a.m. the three sounds through the fog were astonishingly powerful, the 
syren particularly filling all the air with a loud and full sound. There was not the 
slightest difficulty in at once indicating the exact direction from which the sound pro- 
ceeded. 
“ By 9 a.m. the atmosphere had begun to clear in the west, and as the day advanced 
the fog rolled slowly eastward. At 10 a.m. the line of demarcation between fog and 
clear atmosphere was a little to the eastward of the pier ; and there was a marked dif- 
ference between the sounds at this period and those of the early morning, a very sensible 
diminution in power being noticeable. 
“ Mr. Troughton’s report of this last day’s observations is to the following effect : — 
At 8 a.m. dense fog all round ; frosty : steamed out to get upon bearing of E.S.E. from 
lighthouse, i. e. at right angles to the axial line of the syren and horn. 
“At 10.10, supposing that the vessel was not far from the E.S.E. line, and (allowing 
for the set of the tide and distance run as shown by the patent log) the distance from 
the lighthouse being apparently near 11 miles, stopped the vessel and heard syren and 
horn equally powerful, the sounds being thoroughly good and serviceable. 
“ Mr. Troughton further states that he could locate the position from whence the 
sound proceeded with the greatest ease, and that he took his bearing from the South 
Foreland by the aid of the sound alone. 
“At this position a wreck-buoy was dropped, the fog being at the time exceedingly 
thick. 
“At 10.18 the fog began to break, and the sounds were not again heard. 
“ At the Varne light-ship, 12f miles from the lighthouse, the master reports that from 
8 a.m. to 10.30 a.m. they heard the ‘horns distinct but not loud.’ 
“ At the South Sand Head light-ship the sounds were plainly heard on Thursday, 
Friday, and Saturday during the fog.” 
The results here recorded are of the highest importance, for they bring us face to face 
with a dense fog and an actual fog-signal, and confirm in the most satisfactory manner 
the previously recorded observations. The fact of Captain Atkins and Mr. Edwards being 
awakened by the sound of the syren, proves, beyond all our previous experience, the power 
of the sound on the 7th of February. 
It is important also to note that through the same fog the sounds were well heard at 
the South Sand Head light-vessel, which is in the opposite direction from the South 
Foreland, and, as will immediately appear, actually behind the syren. 
It is exceedingly interesting to compare the transmission of sound on February 7 
