190 Mr. 0. Heaviside on the 



doubt it is sometimes true) that, with an intermitter making 

 regular vibrations, we might regard the residual sound as 

 due to the upper partials, and that njiir could be taken as 

 the frequency of the intermitter, and (34 c), (35 c) employed 

 safely, though not with any pretensions to minute accuracy, 

 if circumstances compelled us to ignore the exact methods of 

 true balances, were it not for the fact that this hypothesis 

 sometimes leads to utterly absurd results when experimentally 

 tested. Of this I will give an illustration, and, as we have 

 only to test that intermittences may be regarded as S.H. 

 reversals, simplify by taking R^Rg, L X = L 2 , which makes 

 an exact equal-ratio balance, R 3 = R 4 , L 3 = L 4 . 



Since a steady or slowly varying current does not produce 

 sound in the telephone, if a battery could be treated as an 

 ordinary conductor, we could put it in one of the sides of the 

 quadrilateral and balance it, just like a coil, in spite of its 

 electromotive force. So, let 1 and 2 be equal coils, 3 the 

 battery to be tested, and 4 the balancing coils. I find that a 

 good battery can be very well balanced, though not perfectly, 

 with intermittences, as regards resistance, which is, however, 

 far less with rapid intermittences than with a steady current*. 

 Thus : steady, 2\ ohms ; intermittent (about 500), 1J ohm. 

 Another battery : steady, 166 ohms ; intermittent, 126 ohms. 

 The steady resistances are got by cutting out the intermitter, 

 using a make-and-break instead ; the deflection of a galvano- 

 meter in 5 must be the same whether 6 is in or out. If we 

 leave out the battery in 6, it becomes Mance's method. The 

 sensitiveness is, however, far greater when the battery is not 

 left out, although other effects are then produced. 



So far regarding the resistance. As regards the inductance, 

 or apparent inductance, of batteries, that is, I find, usually 

 negative. That is to say, after bringing the sound to a 

 minimum by means of resistance-adjustment, the residual 

 sound (sometimes considerable) may be quenched by inserting 

 equal coils in branches 3 and 4, and then increasing the 

 inductance of the one containing the battery under test. I 

 selected the battery which showed the greatest negative induc- 

 tance, about J mac, or 500,000 centim., got the best possible 

 silence by adjustment of resistance and inductance, and then 

 found the residual sound could be nearly quenched by allowing 

 induction between the coil in 3 and a silver coin, provided, at 

 the same time, R 4 were a little increased. 



It was naturally suggested by the negative inductance and 



* I am aware that Kohlrausch employs the telephone with intermit- 

 tences to find the resistance of electrolytes, but have no knowledge of how 

 he gets at the true resistance. 



