ON OHM S LAW. 



59 



the tuning-forks, and were at the rate of 60 per second. The resistance of 

 the thin wire was very nearly the same, and it was enclosed in a narrow tube. 

 The four Daniells had run down a good deal, being not quite equivalent to 

 three, and the two had varied in in'oportion. The resistance which balanced 

 the wire was, exclusive of the bridge-wire, 7-25 ohms. 



It will be seen that the effect that was so conspicuous in the first experi- 

 ment scarcely appears here at all. It was in fact so small that its appearance 

 might be due to progress of the balance in the interval between the five 

 observations. 



In the next experiment the wire had a resistance of about 4*4 ohms ; the 

 material was German silver, and the diameter the same as before. The 

 resistance against which it was balanced was a German-silver wire of about 

 •12 centim. diameter, wound on a bobbin, the resistance of which was 4-45 

 ohms. The Daniells had been fresh charged, and were arranged in piles of 

 four and two as usual, the respective internal resistances being about 5 and 3. 

 The small resistance-box was on the left with the thin wire. 



The experiment is marked in the laboratory book as very steady. It will 

 be remarked that the sensibilities are large and well proportioned ; for if 

 we had theoretically perfect adjustment, the sum would have been 156 and 

 the difference 54, as against 170 and 53. The -|- + balance is of course 

 much more delicate than the -f- — ; but even for the latter (6 centimetres 

 o-ivino-, say, 54) we have 8 scale-divisions to a centimetre, so that we may 



rely on our -| balances to about a millimetre. This experiment therefore 



indicates a coincidence of the two balances within -0016 per cent. 



A good many experiments were tried with higher electromotive forces ; but 

 though qualitative results of some interest were got, sufficient steadiness could 

 not be obtained to make the results of use quantitatively. In most of these 

 the thin wire Avas over a red heat ; in fact in many of them the experiment 

 ended with the melting of the wire. In general there appeared to be a good 



