17 



He also referred to other oppida in Kent, especially those at 

 Cobham, Syndale, Bigbury, and Chilham ; and said that he believed 

 one of the latter two had claims to be the oppidum mentioned by 

 Caesar, to which the Britons retreated after he had defeated them 

 on the banks of a river, 12 miles from the Eoman camp. 



OCTOBER 7th. 



Mr. A. Haddon, of the Royal Naval College, Greenwich, read a 

 paper on "Various forms of Telephone." The Lecturer began by 

 briefly explaining the manner in which sound is propagated through 

 air, and then passed on to the conduction of sound through solids. 

 In the historical notice, mention was made of Dr. Page's discovery of 

 the sound given out b)'^ a bar of iron at the moment of magnetisation 

 by a current of electricity, and of the adoption of this discovery by 

 Riess in his improved form of telephone. Ehsha Gray's telephone, 

 in which the variation of the strength of the current was brought 

 about by a wire more or less immersed in a liquid of high resistance 

 was also explained. A telephone, of the type invented by Professor 

 Alexander Graham Bell, was then taken to pieces, and the functions 

 of the different parts, viz., — the magnet, the coil, and the diaphragm, 

 explained. Experiments were shown, to demonstrate the various 

 modes in which a membrane or plate can vibrate. In order to prove 

 the generations of currents in the telephone by the motion of the 

 plate, or of a mass of iron near the end of the magnet, the following 

 experiment was exhibited : — Two telephones, with their diaphragms 

 removed, were placed some distance apart, and connected by wires ; 

 and opposite the free end of each magnet a tuning-fork was placed, 

 both tuning-forks giving the same number of vibrations. When one 

 of the forks was sounded and brought near the end of one of the 

 telephones, the other fork vibrated also. This fact was shown to 

 the audience by allowing a lump of sealing-wax, suspended by a 

 thread, to rest against the end of the distant tuning-fork, and, as 

 soon as that fork vibrated, the sealing-wax was kicked off to some 

 distance. The lecturer then referred to Gower's loud-speaking 

 telephone, in which the magnets are of a horseshoe form, both poleg 



