Chemistry and Physics. 61 
circuit, being called a “transmitter.” Exposed to sound, even 
when quite inaudible to the unaided ear, the resistance of the 
transmitter varies in scnsenmiai of the vibration, thus varying 
the current strength and producing in the telephone a distinct 
’ h t is lying, the 
merest contact with a feather or a camel’s hair pen is distinctly 
heard in the receiver, and both instrumental and vocal sounds are 
transmitted with power. Acting on these facts, Baghes devised 
inch thick, pointed at the ends and supported vertically between 
two blocks of the same carbon which have small cavities hollowed 
out to receive it, the upper end being more blunt than the lower, 
and rounded. The weight of the upright _ is only just st suf 
ficient to make a feeble contact. ith this form of transmitter 
the beating of the pulse, the tick of a watch, the tramp of a fly can 
thus be heard at least a hundred miles from the source of sound. 
In explanation of these facts, the author says: “It is quite evident 
that these effects are due to a difference of pressure at the differ- 
ent points of contact and that they are dependent for the perfec- 
tion of action upon the number of these oats of contact. The 
are not dependent = any apparent difference in the bodies in 
contact but the same body in a state of minute subdivision is 
? 
e results which have been marry by Hughes as above 
described, are clearly ae ene by more than a year by those of 
Edison.* In January, 1877, while sabid in perfecting an 
aa eae telephone, Edison made use of the fact discovered by 
n 1873, that semi-conductors wali the peculiar bane ed of 
* To the center of a 
escri new form of relay based on the gee of th 
ing resistance by pressure, using disks of carbon on th 
the receiving electro-magnet, on which disks the armature r 
*The Speaking Pea bone, Talking Phonograph and other novelties. By 
B. pp. 431, 8vo. New York, 1878. D. Appleton & Co, 
+ Journal of the the Telegraph, x, 163, June, 1877 
