330 
POPULAR SCIENCE REVIEW. 
The Audiometer was exhibited by Dr. Richardson at the meeting of the 
Royal Society on May 22. It consists of two Leclanch^’s cells ; a new 
microphonic key connected with the cells, and with two fixed primary 
coils; and a secondary or induction coil, the terminals of which are 
attached to a telephone. The induction coil moves on a bar between the 
two fixed coils, which is graduated into 200 parts, by which the 
readings of sound are taken. The scale is divided into 20 centims., and each, 
part is subdivided into 10, so that hearing may be tested from zero to 200. 
The fixed coil on the right hand contains 6 metres of wire ; that on the left 
hand contains 100 metres. The secondary coil contains 100 metres of wire. 
In using the instrument, the induction coil is moved along the scale from 
or towards the larger primary as may be required, and the degrees or units 
of sound are read from the scale, the sound being produced by the movement 
of the microphonic key between the battery and the primary coils. 
As a rule, the hearing of right-handed persons is most refined in the right 
ear. The influence of atmospheric pressure is to be detected by this instru- 
ment, the delicacy of hearing diminishing when the barometer is low. The 
effect of practice and of memory in distinguishing sounds has also been 
experimented on. 
The Sphygmophone . — It occurred to Dr. B. W. Richardson, while experi- 
menting with the audiometer, that he might get a secondary or telephonic 
sound from the movements of the pulse at the wrist. He effected this in a 
very simple manner, by adding a microphone to a Pond’s sphymograph. 
He mounts on a slip of talc a thin plate of platinum, and places the talc slip 
in the spliygmograph as if about to take a tracing of the pulse. He connects 
one terminal from a Leclanch6’s cell to the slip of platinum on the talc, and 
the second terminal from the cell to a terminal of the telephone. Then he 
connects the other terminal of the telephone with the metal rod of the 
sphygmograph which supports the talc. The instrument is now ready for 
use. It is placed on the pulse in the ordinary way, and is adjusted, with the 
writing needle thrown back, until a good pulsating movement of the needle 
is secured. When the movement is in full action, the needle is thrown over 
to touch the platinum plate, which it traverses with each pulse-movement 
and completes the connection between the telephone and the battery. The 
needle, in passing over the metallic plate, causes a distinct series of sounds 
from the telephone, which correspond with the movements of the pulse. 
When all is neatly adjusted, the sounds heard are three in number, one long 
sound and two short, corresponding to the systolic push, the arterial recoil, 
and the valvular check. The sounds are singular, as resembling the two 
words “ bother it.” The sounds can be made very loud by increasing the 
battery power. This little instrument is not so good a recorder of the pulse 
as the sphygmograph, but it may be made very useful in a class, for illus- 
trating to a large number of students, at one time, the movements of the 
natural pulse, and the variations which occur in disease. 
