Waves along a Line of Negligible Leakage. 299 



with each experiment. The waves generated by the primary 

 oscillator were about 8'5 metres long, and, when on the line, 

 are of the form represented in fig. 2. 



The electric waves propagated along the line are thus 

 seen to be in the form of a damped train with the large 

 end leading ; the tail after about ten or a dozen waves 

 being almost negligible. The curve of fig. 2 was obtained 



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experimentally by Bjerknes' method, and is identical with 

 that marked E in the paper on "Absorption of Electric 

 Waves"*. 



Method of Determination. — The method used for deter- 

 mining the attenuation of the waves in their transit along 

 the line was the same as that described in the first paper 

 already referred to. It consists essentially of alternately 

 using at the end of the line a bridge which completely absorbs 

 the waves and a bridge which completely reflects them. In 

 the first case the wave-train goes but once past the electro- 

 meter, and gives a deflexion S lf say; in the second case the 

 electrometer is affected by the sum to infinity of two geome- 

 trical progressions due to the forward and return trains re- 

 spectively. Let the consequent deflexion be B 2 . Then the 

 ratio r of B 2 to o\ is a function of the attenuation factor e~ <TX J 

 the reflexion coefficient at the oscillator, p, and the lengths of 

 the line, / : and / 2 , before and after the electrometer respectively. 

 It is convenient, however, to solve the equations first for p 2 

 and 5, where 10~ sx ' = e~ <rX , x' denoting lengths in metres and 

 x lengths in centim. along the line. 



Observations and Results. — The present determination is 

 based upon observations with lengths of 116 metres and 

 65 metres respectively before the electrometer, and 48 metres 

 in each case after. To determine the ratio S 2 /o\ in the second 

 case 41 electrometer- throws were sufficient. These are given 

 in Table I. In the first case, as the sparks of the oscillator 

 were less regular, over a hundred electrometer-throws were 

 taken before the required accuracy was obtained. Table II. 

 summarizes the data and results. 



* Phil. Mag. January 1897, p. 43 ; Proc. Phys. Soc. March 1897, 

 p. 27. 



