298 Dr. E. H. Barton on the Attenuation of Electric 



coils respectively of the induction-coil, of which C has a 

 resistance of 3000 ohms and an inductance of about 20 

 henries. G is the spark-gap, which was adjusted to 2 millim. 

 The wire PGP', measured along the semicircle, was about 

 2 metres. PP' are condenser-plates of zinc 40 centim. diam. 

 placed opposite to and 30 centim. distant from the precisely 

 similar plates S W. The line is represented by S E T T' E' S', 

 and consists of two parallel copper wires 1*5 millim. diam., 

 and kept 8 centim. apart by wood separators at intervals of 

 about one metre. These wood separators are about 12 centim. 

 long, 2*5 centim. wide, and 1*2 centim. thick, and were well 

 saturated in melted paraffin-wax before use. Their resistance 

 was thus raised to something over 60,000 megohms each, 

 which rendered the leakage of the line quite negligible. 

 E E' denotes the electrometer, which has a single plane 

 needle, initially uncharged, and suspended by a fine quartz 

 fibre between two disks attached to the line at E and E'. 

 The needle is therefore electrified by induction whenever 

 a wave passes E E', and its ends are consequently attracted 

 to the disks whatever the sign of their potential-difference. 

 T T' signify the two bridges alternately used at or near the 

 end of the line, namely, (1) the bridge of critical resistance 

 which absorbs the waves completely, and (2) the bridge 

 which reflects them completely. The lengths of the line 

 before and after the electrometer will be stated in connexion 



Fig. 2. 

 Curve showing Wave-Train advancing to the right. 



0-9 



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0-7 

 0-6 

 0-5 

 0-4 

 0'3 



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20 19 18 17 16 15 14 13 12 11 10 9 8 7 



Lengths along wires in metres. 



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