2ba PLEASANT WA YS IN SCIENCE. 



top, and across it, near the top, is stretched a membrane 

 which vibrates synchronously with the aerial vibrations cor- 

 responding to the note. At the middle of the membrane, 

 on its upper surface, is a small disc of metal, connected by 

 a thin strip of copper with the positive pole of the battery at 

 the transmitting station. The disc also, when the machine 

 is about to be put in use, lightly touches a point on a metallic 

 arm, along which (while this contact continues) the electric 

 current passes to the wire communicating with the distant 

 station. At that station the wire is carried in a coil round 

 a straight rod of soft iron suspended horizontally in such a 

 way as to be free to vibrate between two sounding-boards. 

 After forming this coil, the wire which conveys the current 

 passes to the earth-plate and so home. As already explained, 

 while the current passes, the rod of iron is magnetized, but 

 the rod loses its magnetization when the current ceases. 



Now, when a note is sounded in the box at the trans- 

 mitting station, the membrane vibrates, and at each vibration 

 the metal disc is separated from the point which it lightly 

 touches when at rest Thus contact is broken at regular 

 intervals, corresponding to the rate of vibration due to the 

 note. Suppose, for instance, the note C is sounded ; then 

 there are 256 complete vibrations in a second, the electric 

 current is therefore interrupted and renewed, and the bar of 

 soft iron magnetized and demagnetized, 256 times in a second. 

 Now, it had been discovered by Page and Henry that when 

 a bar of iron is rapidly magnetized and demagnetized, it is 

 put into vibrations synchronizing with the interruptions of 

 the current, and therefore emits a note of the same tone as 

 that which has been sounded into the transmitting box. 



Professor Heisler, in his " Lehrbuch der technischen 

 Physik," 1866, wrote of Reuss's telephone : " The instrument 

 is still in its infancy ; however, by the use of batteries of proper 

 strength, it already transmits not only single musical tones, 

 but even the most intricate melodies, sung at one end of the 

 line, to the other, situated at a great distance, and makes 

 them perceptible there with all desirable distinctness." Dr. 



