175 
ON THE TRANSMISSION OF SOUND BY THE 
ATMOSPHERE. 
By JOHN TYNDALL, D.C.L., LL.D., F.R.S. 
T HIS notice embraces the scientific results of an inquiry on 
fog-signals, undertaken at the instance of the Elder 
Brethren of the Trinity House, and communicated, with their 
friendly concurrence, to the Royal Society. 
The investigation was begun on May 19, 1873, and continued 
till July 4. It was resumed on October 8, and continued to 
the end of November. It also includes observations made 
during the dense fog which enveloped London on December 9 
and the succeeding days. 
dongs and bells were excluded from this investigation, in 
consequence of their proved inferiority to other instruments of 
signalling. The experiments were made with trumpets blown 
by powerfully compressed air, with steam-whistles, guns, and a 
steam -syren, associated with a trumpet 16 feet long. 
Daboll’s horn, or trumpet, had been highly spoken of by 
writers on fog-signals= A third-order apparatus of the kind 
had been reported as sending its sound to a distance of from 7 
to 9 miles against the wind, and to a distance of 12 to 14 
miles with the wind. Holmes had improved upon Daboll ; and 
with two instruments of Holmes — not of the third, but of the 
first order — our experiments were made. On May 1 9, at 3 miles 
distance, they became useless as a fog- signal ; at a distance of 4 
miles, with paddles stopped and all on board quiet, they were 
wholly unheard. At a distance of 2 miles from the Foreland 
the whistles tested on May 19 became useless. The twelve 
o’clock gun, fired with a 1 lb. charge at Drop Fort in Dover, 
was well heard on May 19, when the horns and whistles were 
inaudible. On May 20 the permeability of the atmosphere 
had somewhat increased, but the steam-whistle failed to pierce 
it to a depth of 3 miles. At 4 miles the horns, though aided 
by quietness on board, were barely heard. By careful nursing, 
if I may use the expression, the horn-sounds were carried to a 
