40 Messrs. Barton and Bryan on the Absorption of 



"the electricity is all gobbled up at once, so to speak "*. 

 And, a few preliminary difficulties being overcome, this im- 

 portant theoretical conclusion readily received experimental 

 confirmation. 



Experimental Arrangement, — The electric vibrations were 

 generated by an oscillator of the type and size previously 

 used by Mr. V. Bjerknes t and others. The waves, about 8 J 

 metres long, were propagated along a " line " consisting of a 

 pair of parallel copper wires 1*5 mm. in diameter and 8 cm. 

 apart. The waves were detected and relatively measured by 

 an attraction-electrometer made on the principle of that 

 devised by Herr von Geitler J. The length of the line to the 

 electrometer was 116 m. This instrument has a needle of 

 aluminium foil suspended by a quartz fibre between disks 

 which may be connected to the respective wires of the line. 

 On the passage of a wave-train the needle, initially uncharged, 

 is charged inductively, and its ends are accordingly attracted 

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



The electrometer therefore responds by a deflexion of the 

 needle towards its disks. Let us call this a positive deflexion. 

 In addition to the needle just described, and fixed to it in the 

 same vertical plane, is a second similar one, but with its pair of 

 attracting disks so situated that when they alone are connected 

 to the line a negative deflexion ensues. When both needles 

 have their respective disks connected to the line the electro- 

 meter is said to be used differentially. When so used, and with 

 the instrument in adjustment, no deflexion is produced by the 

 simple passage of a wave-train. Suppose now, owing to any- 

 thing on the line which causes reflexion, stationary waves are 

 produced at the electrometer. Then, provided one needle be 

 connected to a point on the line which is a node for the 

 waves, and the other be at a loop, the electrometer must give 

 a deflexion and thus prove that reflexion of the waves has 

 occurred. It is easily seen that when a single needle is used 

 the first throw is proportional to the time-integral of the 

 square of the potential-difference of the two leads of the line 

 at the place to which the disks are connected. 



The electrometer-needle carried a light plane mirror, and 

 the throws were read by a distant telescope and scale. 



Theory of Absorption. — Mr. Heaviside's § theory shows that 



* Loc. cit. p. 127. 



t V. Bjerknes, Wied. Ann. vol. xliv. pp. 519-520 (1891) ; E. H. 

 Barton, Proc. Roy. Soc. vol. liv. p. 86 (1893) j G. U. Yule, Proc. Roy. Soc. 

 vol. liv. p. 97 (1893). 



% Wied. Ann. vol. xlix. p. 188 (1893). 



§ l Electrical Papers/ vol. ii. pp. 132-133. 



