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[July, 
SCIENTIFIC NOTES. 
By far the most prominent event of the quarter has been the discovery 
of the Microphone. The scientific world had scarcely recovered from 
the surprise excited by the wonders of the Telephone and Phonograph, 
when Prof. Hughes, the well-known electrician, announced that the eleCtrical 
resistance of certain bodies was influenced by sonorous vibrations propagated 
in their vicinity, just as selenium is influenced by light, and that in so supreme 
a degree as to magnify sounds of the most delicate nature to such a pitch 
that the tramp of a fly on a wooden box could be distinctly heard. The way 
in which Prof. Hughes discovered this important faCt was the following : — He 
was trying some experiments on the changes which take place in the electrical 
resistance of a strained wire, using for the purpose a closed circuit, including 
a small battery and a Bell Telephone. He noticed that, although no change 
was apparent when the stretched wire. was spoken to, when it broke a rush of 
sound was heard in the receiving Telephone, the noise being repeated when 
the wires were re-united. By simply crossing the broken wires, and placing a 
small weight on the top of them, it was found that sounds uttered close to 
them were repeated in the Telephone. Other conducting materials were tried 
with similar effeCt, some of them — such as gas carbon and pine charcoal — 
being more sensitive than others. The problem solved by Prof. Hughes’s 
discovery is to introduce into an eleCtrical circuit an eleCtrical resistance 
which shall vary in exaCt accord with sonorous vibrations, which are thus 
transformed into eleCtrical vibrations, to appear once more as sound in the 
ear-piece of the Telephone ; in other words, the molecules of conducting 
bodies in molar contact and under pressure are so regulated in their motions 
by the waves of sound in their neighbourhood that they decrease and increase 
the resistance of a circuit to a remarkable degree. A great variety of Micro- 
phones were constructed by Prof. Hughes, of all kinds of materials, each 
having a special range of variation of resistance. Thus a simple stick of 
charcoal resting on another is so sensitive that a fly’s tramp may be distinctly 
heard ; but it would be too delicate for the human voice, the vibrations caused 
by this being too powerful. In transmitting articulate sounds the area and 
the number of the points of contaCt must be increased so as to reduce the 
extreme sensibility of the instrument. For magnifying the human voice 
Prof. Plughes uses a Microphone consisting of a glass tube containing several 
cylinders of pine or willow charcoal in close contaCt, the two end pieces being 
in circuit. Mr. Blyth, F.R.S.E., has succeeded in making a most efficient 
articulating Microphone out of a jam-pot, or a wooden box containing gas- 
cinders : eleCtrical continuity is insured by the ends of the circuit being con- 
nected with two tin plates thrust between the cinders and the side of the 
vessel. In another experiment he found that by wetting the cinders he could 
do away with the battery, while, on the other hand, by using a stronger battery 
he found that the cinder boxes would aCt both as receivers and transmitters, 
thus doing away with the necessity for using a magnetic Telephone. The 
sounds in the latter case were very faint, and not easily distinguished ; but 
the faCt remains that they were transmitted, nothing being in circuit but a 
couple of cinder boxes and two Grove’s cells. Hughes’s Microphone has 
already been applied most successfully as a test for the presence of stone in 
the bladder and foreign solid bodies in the animal tissues. Experiments of a 
very promising nature have also been made with the Microphone as a substi- 
tute for the Stethoscope in lung and heart disease. Mr. W. J. Lancaster, 
F. C.S., has rendered the Microphone still less complicated, by doing away 
with the subsidiary battery, and using the negative, plate of a simple carbon 
