Mr.Toynbeeon the Mode of transmission of Sonorous Undulations. 57 
tained within it, a vibrating tuning-fork C’ placed within a quarter 
of an inch of its free extremity, was heard very distinctly at first, 
and it did not cease to be heard for fifteen seconds. 
Experiment 3.—Three portions of wood, of the same length and 
thickness as that used in the previous experiments, were glued 
together so as to form a triangle somewhat of the shape of the 
stapes; the base of this triangle being placed against the outer 
surface of the tragus, as in the previous experiment, the tuning-fork 
C’ vibrating within a quarter of an inch from its apex was heard for 
twelve seconds. 
Considering, as shown by the above experiments, the great facility 
with which sonorous undulations pass from the air to a solid body, it 
may, I think, be assumed that the undulations in the tympanic cavity 
may be conveyed to the stapes even when this bone is isolated from 
the rest of the chain, and conducted by it to the vestibule; and 
when it is also considered that the absence of all the ossicles, or even 
a fixed condition of the stapes, is productive of deafness, there is 
strong evidence in favour of the opinion that sounds from the 
external meatus cannot reach the labyrinth without the medium of 
the ossicles. 
2. Is there any peculiarity in the conformation of the chain of ossi- 
cles which precludes the passage of sonorous undulations through it? 
This question has also been answered in the affirmative, on account 
of the various planes existing in the chain ; and secondly, on account of 
the joints existing between the several bones composing this chain. 
The following experiments refer to the influence of the varying 
plane of the bones forming the chain, and of its articulations, on the 
progress of sonorous undulations through it :— 
I. Experiments illustrative of the influence of the variety of planes 
in the chain. 
Experiment 1.—Three pieces of wood, each 5 inches in length 
and half an inch thick, were glued together thus | » SO as to 
represent the planes in which the malleus, incus, and stapes are 
arranged in the chain of ossicles, while three similar portions were 
glued end to end so as to form a straight rod. A watch was placed 
in contact with one end of the straight rod, while the other was 
pressed gently against the tragus so as to shut the external meatus. 
The result was that the watch was heard nearly as distinctly as 
when in contact with the ear. When a similar experiment was per- 
formed with the angular portion of wood representing the chain of 
bones, the watch was also heard, but less distinctly than through the 
straight portion. 
Experiment 2.—A tuning-fork C’, being made to vibrate, was 
placed in contact with one extremity of the angular piece of wood, 
the other being placed against the tragus of the ear; and as soon as 
the sound ceased to be heard, the straight portion was substituted, 
when the tuning-fork was again heard, and it continued to be heard 
for about three seconds. 
