AS A VEHICLE OF SOUND. 
187 
are thus sent through the air, the pitch of the note produced depending on the velocity 
of rotation. 
To the syren, trumpets, and whistles were added three guns — an 18-pounder, a 5^-inch 
howitzer, and a 13-inch mortar. In our summer experiments all three were fired; but 
the howitzer having show r n itself superior to the other guns it was chosen in our autumn 
experiments as not only a fair but a favourable representative of this form of signal. 
The charges fired were for the most part those now employed at Holyhead, Lundy 
Island, and the Kish light-vessel — namely, 3 lbs. of powder. Gongs and bells were not 
included in this inquiry, because previous observations had clearly proved their infe- 
riority to the trumpets and whistles. 
A general knowledge of the instruments employed is thus imparted to the reader; 
while the Map on Plate XVII. will furnish him with all necessary information as to the 
position of the localities referred to in the paper. 
On the 19th of May the instruments tested were : — 
On the top of the cliff : 
a. Two brass trumpets or horns, 11 feet 2 inches long, 2 inches in diameter at the 
mouthpiece, and opening out at the other end to a diameter of 22^ inches. They were 
provided with vibrating steel reeds 9 inches long, 2 inches wide, and ^ inch thick, and 
were sounded by air of 18 lbs. pressure. 
b. A whistle, shaped like that of a locomotive, 6 inches in diameter, also sounded by 
air of 18 lbs. pressure. 
c. A steam-whistle, 12 inches in diameter, attached to a boiler, and sounded by steam 
of 64 lbs. pressure. 
At the bottom of the cliff : 
d. Two trumpets or horns, of the same size and arrangement as those above, and 
sounded by air of the same pressure. 
e. A 6-inch air-whistle, similar to the one above, and sounded by the same means. 
The upper instruments were 235 feet above high-water mark, the lower ones 40 feet. 
A vertical distance of 195 feet, therefore, separated the instruments, A shaft, provided 
with a series of twelve ladders, led from the one to the other. 
The trumpets were constructed by that able mechanician, Mr. Holmes, who had them 
throughout under his personal superintendence. They were mounted vertically on the 
reservoir of compressed air ; but within about 2 feet of their extremities they were bent at 
a right angle, so as to present their mouths to the sea (see sketch of horn on Plate XVIII., 
where the steel reeds are also shown). The aim of their constructor was to distribute 
the sound equably over an arc of 180°. To effect this, he placed the horizontal parts of 
the axes of the horns at right angles to each other, the one pointing S.W. by S,, and the 
other S.E. by E., each horn being supposed to cover an arc of 90°. 
The 12-inch steam-whistle was constructed by Mr. Baily, of Manchester, 
Our first experiments with these instruments were a preliminary discipline rather than 
an organized effort at discovery. On May 19 we steamed round the Foreland and out 
2 b 2 
