400 Transactions. — Chemistry. 



The condensers, which are placed at F and D respectively, are used to 

 balance the static induction of the line. On long lines they are most valuable 

 adjuncts, but on short lines do not appear to be necessary. Duplex telegraphy 

 has to thank Mr. Stearns, of America, for this addition. Doubtless, so far as 

 we know at present, and with the present appliances, it would not be possible 

 to work duplex circuits of any length without the aid of the condenser. The 

 condenser is made of a proportional capacity equal to the capacity of the real 

 line. The exact action of the condenser within itself is not known, but I am 

 of the opinion that it acts as a sort of storehouse for the current, receiving a 

 portion of the charge when the current is sent on to the line, and, when the 

 current ceases to flow, gradually discharges itself, and by so doing neutralizes 

 the static discharge of the real line, that is the second flow of the current that 

 is induced in the line in the opposite direction, or the residue of the charge 

 which still clings to the conductor after the first rush of the current has passed. 



I have now described all the conditions under which duplex is worked by 

 the Wheatstone Bridge principle. I have shown how A can telegraph to B 

 without disturbing his own apparatus, and how B can do the same. 



The next step is to describe the effect when both A and B send their 

 currents simultaneously to line, and how it is that the one current does not 

 interfere with the other when both are on the line at once. The question is, 

 do they pass one another ? If not, how does A's signal record itself at B, and 

 vice versd, without the one interfering with the other, or mixing up, or clashing 

 with each other. 



It has been stated " that the two currents do not pass one another as has 

 been imagined, but that, when both stations signal at the same time, the 

 current sent by either station acts upon the distant instrument by deter- 

 mining whether the line or the rheostat (the artificial resistance) shall offer 

 the easier path for the currents originating there." 



The results of an experiment I made by the aid of two induction coils 

 (each coil giving a spark of IJ inch in air), have led me, however, to a some- 

 what different conclusion, and I am inclined to think that the currents sent 

 from either end do actually pass one another, or at any rate exchange impulses, 

 and so record the opposite signal. If the currents, instead of passing one 

 another, simply exchange impulses, they only obey one of the laws of motion ; 

 for if wo treat the two currents as two elastic bodies moving with equal 

 velocities, and in opposite directions, at the point of contact they are each 

 acted upon in their turn, and in the opposite direction, for as the motion of 

 two bodies when started from a state of rest is in the direction given them by 

 their first impulse, any change in direction after collision from that first taken 

 must therefore bo duo to an exchange of force or impulse at the time of such 

 collision. 



