Investigation of the Simple Coherer. 275 



circuit is not completed. If the radiating source is near, as 

 in the following experiments, coherence occurs at once: 

 i. e., without capacity and self-induction in the receiving 

 system being in any way changed with a view to resonate the 

 vibrations from the source. 



The spark-gap was placed at distances of from 50 cm. to 

 3 cm. from the contact ; and it was customary to make one 

 spark only by pushing the induction-coil hammer forward 

 once. Sometimes more sparks were used, but in all cases 

 the amount of discharge was in this way w 7 ell under control. 



The process adopted was as follows : — 



(1) Bring the wires together to firm contact, noting the 

 resistance in the galvanometer-circuit R.T. There is no 

 coherence and no current through the contact. 



(2) Pass the spark ; coherence at once occurs, and the 

 voltmeter and ammeter give definite steady readings which 

 are recorded. 



(3) Change the galvanometer-current till, the resistance 

 being R.C., the wires are sundered, as shown by the spot 

 on the scale moving. 



(4) Bring the wires together as in (1), the resistance R.T, 

 is the same as before; but there is an important change, for 

 on the wires touching this time they will almost invariably be 

 found to cohere, a current passing. Read the ammeter and 

 voltmeter. 



By continuing the process of u make " and " break " the 

 coherence caused by the original one spark will gradually die 

 out. When all traces of it have gone a fresh set may be 

 taken. 



We have then this ascertained fact, that whatever physical 

 change occurs in coherence — whether mere fusion, allotropic 

 change, or the formation of a string of particles as a " bridge " 

 — there is associated with it some polarization or a change 

 simulating polarization. This change of the surface particles 

 departs after a few " makes " and " breaks," leaving the sur- 

 face quite normal. Let us call this change Orientation, leaving 

 for the present any explanation or conception of it. 



There are four distinct sets of results for orientation 

 according to the methods of examining it ; they will be given 

 in the four following sections. 



6 a. Direct Currents. 



In this section the current is always sent through the contact 



in one direction and is constant in strength, about £$ ampere. 



The following table consists of five parts corresponding to 



