74 Professor Oliver Lodge on Coherers. [Feb. 24, 



up gaps, and were then found to have cohered ; for if the superfluous 

 filings were then gently removed, a continuous chain of irregular 

 shape remained reaching from one terminal to the other. By 

 suitably choosing the filings their motion when subjected to very 

 slight electric sparks can readily thus be seen, and if subsequently a 

 point be used to sweep them sideways, they are found to be quite in 

 a different condition to ordinary unelectrified filings, for they are 

 matted together into a sort of coherent mass just like the dust 

 particles in a bell-jar under the influence of an electrified point, or 

 somewhat like iron filings in a magnetic field. A stronger spark often 

 destroys this cohesion, scattering the particles asunder, and produc- 

 ing somewhat the same effect as a mechanical tap, though for a 

 different reason. Filings thus electrically disorganised are not 

 usually in a sensitive condition. A set of large brass shavings on a 

 flat surface, with sparks sent through them, at first show lines of 

 spark in all directions, but gradually under the cohering influence 

 are aide to close up and presently conduct the discharge without 

 visible manifestation. 



Thus the process going on more or less in coherers, either the 

 single-point or the multiple point kind, can be made to some extent 

 apparent to the eye. 



Some of the old apparatus used by the lecturer to send signals by 

 Hertz waves and coherers over small distances (the now so-called 

 wireless telegraphy) which had been exhibited to the Institution on 

 Friday evening, June 1st, 1894, were once more exhibited, the re- 

 ceiver being carried about into different parts of the room : but this 

 method of signalling has become w T ell known and developed under 

 the auspices of Signor Marconi, who has succeeded in telegraphing 

 by its means across the 6ea over distances up to twenty or thirty 

 miles. 



[0. L.] 



