1902.] on the Progress of Electric Space Telegraphy. 203 



dition of non-conductivity when in a sensitive state is obtained. 

 Coherers have lately been tried which will work to a certain extent 

 satisfactorily without the necessity of employing any tapper or 

 decoherer in connection with them. Nearly all are dependent on the 

 use of a carbon microphonic contact or contacts which possess the 

 curious quality of partially re-acquiring spontaneously their high 

 resistance condition after the effect of the electrical oscillations has 

 ceased. This enables one to obtain a far greater speed of reception 

 than is possible by means of a mechanically-tapped coherer, the inertia 

 of the relay and tapper which are used in connection with it being 

 necessarily sluggish in their action. In all these self-decohering 

 coherers a telephone which is affected by the variations of the electric 

 current, caused by the changes in conductivity of the coherer, is used 

 in place of the recording instrument. It has not yet been found 

 possible, so far as I am aware, to actuate a recording instrument or a 

 relay by means of a self-restoring coherer. The late Prof. Hughes 

 was the first, I believe, to experiment with and receive signals on one 

 of these coherers associated with a telephone. His experiments were 

 carried out as early as 1879, and I regret that this pioneer work of 

 his is not more generally known. Other self-restoring coherers were 

 proposed by Professors Tommasina, Popoff, and others, but one which 

 has given good results when syntonic effects were not aimed at was 

 (according to official information communicated to me) designed by 

 the technical personnel of the Italian navy. This coherer, at the 

 request of the Italian Government, I tested during numerous experi- 

 ments. It consists of a glass tube containing plugs of carbon or 

 iron with between them a globule of mercury. Lieutenant Solari, 

 who brought me this coherer, asked me to call it the " Italian Navy 

 Coherer." Recently, however, a technical paper gave out that a 

 signalman in the Italian navy was the inventor of the improved 

 coberer, and I was at once accused in certain quarters of suppressing 

 the alleged inventor's name. I therefore wrote to the Italian 

 Minister of Marine, Admiral Morin, asking him to make an autho- 

 ritative statement, to which I could refer in the course of this address, 

 of the views of the Italian Admiralty on the matter. The head of 

 the Italian navy was good enough to reply to me by a letter, dated 

 the 4th inst., in which he makes the following statement, which I 

 have translated from the original Italian : — " The coherer has been 

 with good reason baptised with the name of ' Italian Navy Coherer,' 

 as it must be considered fruit of the work of various individuals in 

 the Eoyal Navy and not that of one." These non-tapped coherers 

 have not been found to be sufficiently reliable for regular or com- 

 mercial work. They have a way of cohering permanently when 

 subjected to the action of strong electrical waves or atmospheric 

 electrical disturbances, and have also an unpleasant tendency towards 

 suspending action in the middle of a message. The fact that their 

 electrical resistance is low and always varying, when in a sensitive 

 state, causes them to be unsatisfactory for the reasons I have already 



